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The Aleutian-Kamchatka Trench Convergence: An Investigation Of Lithospheric Plate Interaction In The Light Of Modern Geotectonic Theory

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The Aleutian-Kamchatka Trench Convergence: An Investigation Of Lithospheric Plate Interaction In The Light Of Modern Geotectonic Theory

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Content THE ALEUTIAN-KAMCHATKA TRENCH CONVERGENCE An Investigation of Lithospheric Plate Interaction in the Light of Modem Geotectonic Theory by Edwin Conger Buffington A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (Geological Sciences) June 1973 INFORMATION TO USERS This material was produced from a microfilm copy of the original document. While the mo>t advanced technological moans to photogaph and raproduoa this document have bean usad. the quality is heavily dependent upon the quality of the original submitted. The following explanation of techniques is provided to help you understand markings or patterns which may appear on this reproduction. 1. The sign or "target" for pages apparently lacking from the document photographed is "Missing P a p U j". If it was possible to obtain the missing page(s) or section, they are spliced into the film along with adjacent pages. This may have nocessitated cutting thru an image and duplicating adjacent pages to insure you complete continuity. 2. When ar. image on the film is obliterated with a large round Mack mark, it is an indication that the photographer suspected that the copy may have moved during exposure and thus cause a blurred image. You will find a good image of the pegs in the Adjacent frame. 3. Whan a map, drawing or chart, etc., was part of the material being photographed the photographer followed a definite method in "sectioning" the material. It is customary to begin photoing at the upper left hand corner of a large dieet and to continue photoing from left to ri(dit *n actual sections w ith a small overlap. If necessary, sectioning is continued again — beginning below tha first row and continuing on until complete. 4. The m ajority of users indicate that the textual content is of greetest value, however, a somewhat higher quality reproduction could be made from "photogrephs" if essential to tha understanding of the dissertation. Silver prints of "photographs" may be ordered at additional charge by writing the Order Department, giving the catalog number, title, author and specific pegas you wish reproduced. 6. PLEASE NOTE: Some pages may have indistinct print. Filmed as received. Xerox University M icrofilm s 300 North Zaob Road Aim Arbor, UlcMgon 4*106 I I i 73-31,330 BUFFINGTON, Edwin Conger, 1920- THE ALEUTIAN-KAMCHATKA TRENCH CONVERGENCE: AN INVESTIGATION OF LITHOSPHERIC PLATE INTERACTION } IN THE LIGHT OF MODERN GEOTECTONIC THEORY. University of Southern California, Ph.D., 1973 Geology University M icrofilm s, A XEROX C om pany, Ann A rbor, M ichigan TH IS DISSERTATION HAS BEEN M ICRO FILM ED EXACTLY AS RECEIVED. UNIVERSITY OF SOUTHERN CALIFORNIA THE GRADUATE SCHOOL. UNIVERSITY PARK LOS ANQELEE. CALIFORNIA *0 0 0 7 This dissertation, written by Edwin .Congsr Buf f ington........ under the direction of A..in.. Dissertation C om mittee, and approved by a ll its members, has been presented to and accepted by The G radu ate School, in p artial fulfillm ent of require ments of the degree of D O C T O R O F P H I L O S O P H Y D*mm ATI ON COMMITTEE TH E \ L EUTIA X - KA M C H ATK A COXVERGEXCE scale v e r t ic a l EXAGGERATION 10 1 M THO M APN tC D M V IM IT t t u M H O tlH M INDEX MAP I u s g eo lo g ic al s u r v e y Frontispiece Orthographic drawing of the Aleutian- Kamchatka Trench Convergence. This three- dimensional sQale representation was con structed by T. R. Alpha using a method dis cussed by Alpha and Winter (1971). The two converging trenches and the contained "arrowhead*1 shaped segment of northwest Pacific sea-floor are centered In the draw ing. The Kamchatka Peninsula at the left extends northward to eastern Siberia. The north-south trending Shirshov Ridge extends south from Cape Olyutorski dividing the deep Bering Sea into the Kamchatka Basin and the Aleutian Basin. ill CONTENTS Page ABSTRACT ........................................ INTRODUCTION.............................. 1 Background........................... 1 Statement of objectives ................... 13 Acknowledgments.......... 16 FIELD MEASUREMENT AT SEA................. 18 Aleutian-Bering Sea Expedition of 1970 . . . 18 Measurements and sampling........ .. • • . 19 Continuous seismic reflection profiling 19 Magnetic measurements ............... . 22 Navigation....................... 22 Dredging.......................... 25 Coring............................ 25 REDUCTION OF DATA ASHORE ............. 26 Seismic reflection records ................. 26 Magnetic d a t a ....................... 30 Navigational data ............... 31 BATHYMETRIC. GEOLOGIC AND TECTONIC SETTING . . . 33 General.............................. 33 Stratigraphlc framework............. 34 V iv Page Western Aleutian Ridge and Komandorsklyes . 36 General............................. . 36 Exposed Western Aleutian Ridge .... 40 Komandorskiye Islands • . . • . . • 41 Near Islands..................... 48 Submerged Western Aleutian Ridge . . . 52 Aleutian Terrace ..................... 57 Aleutian Trench........................ 62 Kamchatka.................................. 72 Kamchatka Peninsula ................... 72 Kamchatka Terrace..................... 86 Kuril-Kamchatka Trench 89 Kuril Island C h a i n ................... 94 Sea-floor outlined by trench convergence . 96 RESULTS--INTERPRETATIONS AND IMPLICATIONS OF THE GEOLOGICAL AND GEOPHYSICAL DATA .... 108 Sediment thickness and distribution .... 108 Oceanic areas Ill JOIDES 1 9 2 ............................ 132 Trenches ................... •.... 132 Sedimentation rates................... 135 Peninsular and insular margins • • • • 138 Aleutian and Kamchatka Shelves • . 138 v Page Aleutian and Kamchatka Terraces • • 139 Inner trench w a l l s ........ 141 Structure....................... 146 Deep sea a r e a s ................. 146 Trench floors.......... - 147 Peninsular and insular slopes......... 149 DISCUSSION AND CONCLUSIONS............. 156 General.............................. 156 Models for plate movement in the North Pacific.......................... 157 Continuous motion model ............... 157 Discontinuous motion model ........ . 160 Models of little or no motion • • , • • 163 Emergence model................. 169 Discussion of models and sedimentation . . 172 Conclusions on plate motion ............... 180 The North American-Eurasian Plate boundary 181 The problem..................... 181 Evidence............ 182 Conclusion..................... 184 Unsolved problems................... 184 Western Aleutian Trench........ 184 Empty Kamchatka Trench........ 186 APPENDICES.............................. 205 vi ILLUSTRATIONS Figure Page 1. Mercator chart of world showing major and minor plates, trenches, ridge axes and areas of seismicity..................... 4 2. Regional chart of the North Pacific Ocean, the Bering Sea, the Aleutian Arc, and eastern Kamchatka ....................... 11 3. Generalized chart of the North Pacific Ocean showing the study a r e a ........... 14 4. Tectonic zoning of Kamchatka........... 75 5. Surface sediment distribution in trench convergence a r e a ....................... 103 6. Curve for correcting echo sounder depth to true depth ..................... 114 7. Curve for determining water velocity from true depth................. 125 8. Isopach chart of oceanic pelaglcs in the convergence area • 127 9. Trench burial by slumping! diagrams show ing how subbottom reflectors could go under inner trench walls without appeal ing to subduetlon....................... 154 vli TABLES Table Page 1. Distances of Individual seismic lines . • 20 2. Summary of retrieved magnetic data • ■ » 23 3. Vertical exaggeration on seismic pro filing records......................... 28 4. Characteristics of Early and Late Marine Series, Western Aleutian R i dge........ 37 5. Summary of stratigraphy of the Korean- dorskiye Islands * . • • ............ 43 6. Summary of stratigraphy of the Near Islands............................. 50 7. Data for determination of layer thickness of oceanic pelagics (Layer 1) . . • . • • 116 8. Minimum thickness of turbidites in Western Aleutian Trench................. 131 9. Sedimentation rates at JOIDES Hole 192 (Meijl Guyot) ........................... 134 viil PLATES Plate Page 1. Bathymetric chart of the Northwest Pacific (from Chase and others, 1970) with satellite navigation plot of ship's track............. * In pocket 2. Seismic Reflection Profile - Line B-30, Shallow Part In pocket 3. Interpretative Overlay - Line B-30, Shallow Part In pocket 4. Seismic Reflection Profile - Line B-30, Deep P a r t In pocket 5. Interpretative Overlay - Line B-30, Deep P a r t In pocket 6. Seismic Reflection Profile - Lines B- 31, 32, 33, 34, 35 In pocket 7. Interpretative Overlay - Lines B-31, 32, 33, 34, 35 In pocket 8. Seismic Reflection Profile - Line B-36 In pocket 9. Interpretative Overlay - Line B-36 . . In pocket 10. Seismic Reflection Profile - Line B-37 In pocket 11. Interpretative Overlay - Line B-37 . . In pocket 12. Seismic Reflection Profile - Lines B- 38, 39, 40, 41 In pocket 13. Interpretative Overlay • Lines B-38, 39, 40, 41 In pocket 14. Seismic Reflection Profile - Lines B-42, 43 In pocket 15. Interpretative Overlay - Lines B-42, 4 3 In pocket ix Plate Page 16, Seismic Reflection Profiling - Line B-44 . . In pocket 17. Interpretative Overlay - Line B-44 f t In pocket 18. Seismic B-45 . . Reflection Profile - Line In pocket 19. Interpretative Overlay - Line B-45 f t In pocket 20. Seismic Reflection Profile - Line B 46 In pocket 21. Interpretative Overlay - Line B-46 f t In pocket 22. Seismic Reflection Profile - Line B*47 In pocket 23. Interpretative Overlay - Line B-47 f t In pocket 24. Seismic Reflection Profile - Line B«48 In pocket 25. Interpretative Overlay - Line B-48 a In pocket 26. Magnetic Profiles - Line B- 30 • * f t In pocket 27. Magnetic Profiles - Line B- 31 • f t f t In pocket 28. Magnet1c Profiles - Line B- 32 * f t • In pocket 29. Magnetic Profiles - Line B-33 # • • In pocket 30. Magnetic Profiles - Line B- 34 f t • • In pocket 31. Magnetic Profiles - Line B-35 f t f t f t In pocket 32. Magnetic Profiles - Line B-36 ■ « ■ In pocket 33. Magnetic Profiles - Line B-37 « • • In pocket 34. Magnetic Profiles - Line B-38 f t f t f t In pocket 35. Magnetic Profiles - Line B-43 f t • • In pocket 36. Magnetic Profiles - Line B-44 f t f t f t In pocket 37. Magnetic Profiles - Line B-45 f t f t • In pocket x Plate Page 38. Magnetic Profiles - Line B-46 .... In pocket 39. Magnetic Profiles - Line B-47 .... In pocket 40. Magnetic Profiles - Line B-48 .... In pocket 41. Magnetic Profiles - Line B-49 .... In pocket xi ABSTRACT The Aleutian and the Kuril-Kamchatka trenches in the northwest Pacific and the wedge-shaped area of oceanic crust outlined by their convergence have been examined by seismic reflection profiling techniques to test the valid ity of several models of crustal plate movement currently invoked for that area. The New Global Tectonics is ac cepted as an excellent working hypothesis and background for the test. Reflection profiling records show structures and strong subbottom reflectors on four crossings of the Kuril-Kamchatka trench which may be interpreted as (1) off-scrapings on the landward wall of the trench of Neo gene pelagic sediments from a subducting Pacific plate or (2) the surface of the oceanic acoustic basement and over- lying pelagics burled beneath sediment slumped from the landward wall of the trench. In either caset the top of the west-dipping acoustic basement (Layer 2} passes under the trench. The first interpretation is the preferred one. This evidence supports the basic idea that a northwesterly migrating Pacific plate is underthrusting Kamchatka. Six crossings of the western Aleutian trench and the adjoining seaward wall of the Aleutian Ridge fall to reveal any similar structures suggesting crustal under- thrusting. Instead, the idea of strike-siip relationships between the American plate north of the Aleutian trench and the Pacific plate to the south is reinforced by features within the trench zone which may be explained by oblique pull-apart resulting from strike slip. For ex ample, rock bodies Interpreted as slices of oceanic pelagics (Layer 1) are found at several places at the foot of the Aleutian Ridge. They are separated from the oceanic sea-floor by flat turbidltes of the trench but appear to be topographically unrelated to the Aleutian Ridge. Secondary turbldlte channels, measurably higher than the trench floor but probably Interconnected with it, can be observed. The Impression is of a zone of sags and ridges. The central of three closely adjacent crossings of the Aleutian trench at longitude 170° E shows no turbidltes while the two adjoining crossings have well- developed flat floors. Local uplift is a possible inter- Jtil pretation. The evidence la suggestive and corroborative rather than conclusive. The ocean floor seaward of the two trenches com prises a thick (up to 1.5 km) section of pelagic and hemlpelaglc sediment (Layer 1) which lies on a clearly discernible acoustic basement (Layer 2). J01DES (Joint Oceanographic Institution Deep Earth Sampling) hole 192, drilled on top of Nelji guyot In the center of the area, provides an excellent basis for dating the pelagics and establishing sedimentation rates. Analysis of measured thicknesses of pelagics and heml-pelagics by establishing Isopach zones suggests that the sediments of the conver gence area originated primarily from terrestrial sources on Kamchatka to the northwest. They lie In a crude tongue which has its thickest point at the convergence proper and thins to the southeast. The sediments are much thicker northeast of the Emperor Seamounts which roughly divide the area on a northwest trend toward Kam chatka Just south of the convergence. The rate of sedi mentation (as determined at J01DES 192 and extrapolated to the adjoining sea-floor) requires that the area south of the convergence be reasonably close to terrestrial sediment sources since the middle Miocene. This permits only a few hundreds of kilometers of travel for the Pacific plate subsequent to that time. The observed thickness of sediment could not have been accumulated at deep-sea sedimentation rates which would be found in the north-central Pacific since the middle Miocene. Thus, the evidence supports models of plate movement which in clude strike-slip movement along the western Aleutian trench and crustal underthrusting along the Kuril- Kamchatka trench, but only relatively short travel of the Pacific plate to the northwest since the middle Miocene. Continuous motion models for the Pacific plate which in volve thousands of kilometers of travel in the Tertiary are not considered appropriate. A variety of evidence suggests that the American plate does not terminate in the Bering Sea with a boundary extending northward from the Juncture of the Aleutian and Kuril-Kamchatka trenches, but that it Includes Kamchatka, part of eastern Siberia, and perhaps the northern Kuril Islands. The Kuril Islands, the Kamchatka Peninsula, and Komanforskiye and Near Islands in the western Aleutians all have a broad common geologic history through the Tertiary with roughly correlative llthologlcal and oro- genlc events. Structures, or clues to structures, indica- x 111 tlve of a tectonic boundary between the Komandorsk lyes and Kamchatka are lacking• Lithologies and flora common to Kamchatka and the Komandorsklyes are reported by Russian geologists* A suspected land bridge between Cape Kamchatskly on Kamchatka and Bering Island has also been reported. The evidence to prove the absence of a boundary In this location Is not conclusive( but it Is strongly suggestive. The continuing existence of the Aleutian trench in its western segment, where strike-slip activity is pre sumed! is an enigma. Without the continuing force of a subducting plate to maintain lsostatlc imbalance! com pensation should have occurred and the trench should have lost its present topographic expression. x i v INTRODUCTION Background In Che discipline of the geological sciences Che lace 1950's, 1960's and early 1970*s are narked by Che appearance and rapid, almost complete, acceptance of hypothesis which has been named the "New Global Tectonics•** It is entirely possible that no single hypothesis since Darwin's (1859) ideas on natural selection, evolution and the origin of species, has so completely captured the enthusiasm and interest of the earth sciences fraternity. The "New Global Tectonics'* offers a comprehensive, global and historical explanation for the present and past posi tion of the earth's continents and ocean basins, for their tectonic interrelationships. It Is compounded of a wide variety of pre-existing ideas, theories and hypotheses, some of them quite old (Davis and others, in press) and new data on paleomagnetlsm, magnetic patterns in the ocean basins, heat flow through oceanic crust, the earth's seismicity and deep-sea bathymetry and gravity. The greater part of this new data has become possible only through technological advances post-dating World War II. The "New Global Tectonics" incorporates and pro- 1 2 poses intriguing explanations for unresolved elements of the old continental-drift theory, the relations of island arcs and marginal trenches, deep-sea sediment distribution and heat-flow anomalies, the overall distribution of seismic activity in the earth's crust and mantle and the relatively new concept of sea-floor spreading. The hypothesis began to develop during the late 1950's, when the time-honored, but highly controversial, and dominantly rejected hypothesis of continental drift, originally conceived and energetically proselytized by Alfred Wegener (1929), was resurrected and revitalized. This revitalisation was given impetus by the concept of sea-floor rereading (Hess, 1960, 1962i Dietz, 1961) even though the concept of sea-floor spreading supplanted Wegener's idea of "continental-crust ships plowing through a sea of plastic mantle" with the notion of "conveyor- belt" mechanics. Shortly after the concept of sea-floor spreading was espoused* the Importance of magnetic patterns recorded from the sea-floor and their relation to spreading was underlined (Vine and Matthews, 1963i Morley and Larochelle, 1964). This was followed by the concept of transform faults proposed by Wilson (1965a). The various concepts and ideas intermingled at an Increasing rate until they were "integrated" in a series of papers with which the "revelation" of the "New Global Tectonics" hypothesis is most commonly identified (Isacks and others* 19681 Morgan, 1968% LePichan, 1968). Because the "New Global Tectonics'* is based on the idea that the earth's crust comprises at least six major and perhaps as many as fifteen or twenty* minor rigid plates (lithosphere) (Fig* 1) which move about on a mobile substrate (asthenosphere), the descriptive phrase "plate tectonics" has become extremely popular. The terms "plate tectonics," "plate tectonic hypothesis," and "plate theory" are essentially synonymous with the "New Global Tectonics," but are now more widely used as "New Global Tectonics” reverts to more or less of a generic status as a descriptive term. This is understandable because the entire hypothesis seeks to explain how the various plates relate to one another. In many publications the term "plate tectonic hypothesis” has been replaced by the term "plate tectonic theory," an unconscious, or perhaps even deliberate acknowledgment of the status the concept should merit. *Dewey (1972) identifies 14 minor plates (Fig. 1), 4 with uncertain boundaries, but fails to consider the Farol- lon plate of some authors, which appears to be controver sial, and the Kula plate which may have existed once, but is now totally subducted. Other minor plates not Included by Dewey but named and identified (see Atwater, 1970) are the Rivera and Juan de Fuca. As the plate tectonic hypo thesis develops, more and more minor plates are reported. Figure X. Mercator chart of the world showing the major and minor llthospherlc plates, zones of crustal growth and consumption, and other elements of the "New Global Tectonics" hypothesis. On this chart major plates are the Euraslan» the African, the North American* the South American, the Pacific and the Australian. Minor plates are the Solomons, Bismark, Philippine, Antarctic, Fiji, Gorda, Cocos, Nazca, Caribbean, Adriatic, Hellenic, Turkish, Iran, and Arabian. Many authors do not separate the North and South American plates*- considering them one plate* They also consider the Antarctic plate a major plate. These differences are relatively academic, a matter of definition and subject to constant change as new data become available (after Dewey, 1972). 4 6 The dynamic nature of the forces appealed to by the plate tectonic hypothesis Is characterized by the presumption that the plates constituting the earth's lithosphere are mobile--that they are moving now or have moved since the beginning of the Mesozoic--at velocities which, geologically, are quite rapid* The plates move apart from one another with new crust being formed in the resulting gap* The locus of this separation is considered by some to mark the surface manifestation of upwelllng portions of two adjacent subcrustal convection cells In the asthenosphere. More recent proposals (Howell, 1970t Kane, 1972) suggest that the impelling force may be rotational inertia, In fact, a Corlolls force. This theory has not evoked much discusslon or received general approval. However, a suggestion by Morgan (1971) that plates are driven by convection "plumes” of primordial material originating in the lower mantle and rising up to the asthenosphere to flow radially away as horizontal cur rents is provoking considerable Interest. Actually the problem of the driving force is far from solved. For tunately the theory itself can be considered without re quiring knowledge of the impelling force. Thus, the geological and geophysical data in hand permit the inter pretation that plates encroach on one another with one plate underthrustIng (or overthrusting) the other. In this case, lithosphere Is consumed, or subducted, as It is 7 forced downward to be reassimilated with the astheno- sphere. And* finally* plates move laterally with re spect to one another, neither consuming nor creating crust. This type of motion customarily takes place along trans form faults (Wilson, 1965a), The "New Global Tectonics" is by no means univer sally accepted although the number of strong dissenters seems to constitute only a small percentage of the geological fraternity. Opinions range all the way from essentially total disagreement (e.g., Meyerhoff, 1969a,b| 1970a,b| Meyer hof f and Meyerhoff, 1972a,b| Meyerhoff and others, 1972t Beloussov, 1969, 1970| Wesson, 1970| Mantura, 1972) through "objective” assessments of "pros” and "cons" (e.g., llich, 1972) and acceptance with mild reservations stemming from observations that do not support the theory (e.g., Scholl and others, 1968, 1970b% Gllluly, 1971) to hyper-enthusiastic, unqualified acceptance almost as an article of faith. The writer feels that the "New Global Tectonics" is an outstanding working hypothesis and, as Gilluly (1971, p. 2383) stated, "about as well demonstrated as anything ever is in geology." It explains infinitely more questions than it poses, and while, as Implied an a pre vious page, it has a major defect— the absence of an easily supportable explanation for a causative force or 8 mechanism--the defect is far from fatal and the hypothesis can be used and developed almost independently of the de fect . The six major plates in the "plate tectonic" hypothesis are the Eurasian* the Pacific, the Australian, the American, the Antarctic and the African (Fig. 1). The American plate, the Pacific plate, and possibly the Eurasian plate meet near the Juncture of the Aleutian and Kamchatka* trenches Just off the peninsula of Kamchatka in the northwest Pacific Ocean. The general consensus of most students of this area (e.g., Oliver and others, 1969| Stauder, 1968a,bi Atwater, 1970t Grow and Atwater, 1970) is that the Pacific plate is moving in a northwest direction, although the rate and duration in geologic time of the motion is uncertain. These authors also be lieve that the Pacific plate is underthrusting the Eurasian plate and the American plate along the length of * Geographically, the Kuril trench and the Kamchat ka trench are the same. In recent cartography of Pacific Ocean bathymetry (Chase and others, 1970) the northern part of the Kuril trench, specifically that part off Kam chatka, is labeled the Kamchatka trench. However, the Bathymetric Atlas of the North Central Pacific Ocean (NAVOCEANO, 1971), which is identical to the Chase chart and was, in fact, constructed by Chase and others for the Naval Oceanographic Office, labels it the Kuril trench. In the Russian literature, the trench is frequently called the Kuril-Kamchatka trench or depression. In this dis sertation the situation is resolved by using all the names interchangeably, recognizing their complete synonymy. 9 both these trenches, with the exception of the western- dost segment of the Aleutian trench as discussed sub sequently. Evidence for underthrusting Is primarily seismic and based on the conclusion that compression phenomena are occurring in a northwest direction as estab lished by first motion studies (Stauder, 1968a,bi Cormier, 1972). In addition, it has been suggested that oceanic crust can be seen dipping under the north (inner) wall of the Aleutian trench at about longitude 180° (Holmes and others, 1972), a suggestion questioned by Harlow and others (1973b). The arcuate Aleutian trench can be divided into three geomorphologic segments (von Huene and Shor, 1969) with easternmost portions trending to the northeast and east, the central portion trending from northeast to east-west to northwest, and the western portion trending strongly to the northwest. Thus, the proposed northwest motion of the Pacific plate encounters the eastern portion of the trench at right angles and the central portion ob liquely, while paralleling the'western portion. Because the Kuril-Kamchatka trench trends northeasterly also, the motion of the Pacific plate Is normal to it. The in ference is that the American plate is not being under thrust by the Pacific plate along the western segment of the Aleutian Arc, but rather that the relations are those of a right-lateral strlke-sllp or transform fault. The Kuril-Kamchatka and the Aleutian trenches join sharply, and terminate at their point of joining just south of Cape Kamchatskly (Fig. 2| PI. 1). No two major trenches elsewhere in the Pacific have a junction as sharply defined as that of the Kuril-Kamchatka and Aleutian trenches. The Emperor Seamounts chain, an aseismlc vol canic ridge, trends northwesterly toward this Junction, but appears to bend westward toward Kamchatka Just short of it. Investigations by Wilson (1965b), Morgan (1971) and Jackson and others (1972) led to the conclusion that the Emperor Seamounts Chain and the Hawaiian Island Chain, which Join in a giant elbow 2550 km to the south of the trench juncture, mark the trail of the Pacific plate as it moved across a Mhot spot" in the asthenosphere, a spot which is presently Just northeast of the Island of Hawaii, An enigma posed by the relationships outlined Is the lack of a clear-cut boundary between the American and Eurasian plates* The spatial relations of each with re spect to the Pacific plate are relatively clear, but little obvious evidence is apparent of a boundary between, if they are indeed separate entities* Perhaps the boundary extends north from the juncture with no current seismic manifestation (i.e., the area is now selsmlcally inactive). A preferable alternative suggested by Churkin (1972) is that the boundary extends southward from the G«kkel Ridge in the Arctic Ocean (a probable spreading center), across Figure 2 Regional chart of the North Pacific Ocean* the Bering Sea* the Aleutian Arc, and eastern Kamchatka. 11 cooc r i ' ! ' \ 1 \ \ • \ • • . \ \ S &3 h O • * , \ 1 0 £ , - / ( ■ • no* i?AW ount chain 0 o % O , O O ? jA lL ^ 0 4 J *v I \ f ' \ ** I o V • V i! i *• o 13 the region of Yakutia in Northeast Siberia, and to a vaguely defined Juncture with the Pacific'Eurasian bound ary somewhere near southern Kamchatka. Statement of Objectives The object of this dissertation is to investigate the interrelationship of the Aleutian Island Arc and trench, the Kuril-Kamchatka trench and peninsula, the Emperor Seamounts Chain, and the Pacific plate where they meet in the northwest Pacific (Figs. 1, 2, 3). This broadly stated objective includes several more specific goals, vizi 1. To examine the evidence for crustal under- thrusting (subduction) in the Kuril-Kamchatka and Aleutian trenches as deduced from known geophysical and geological relationships between the Kamchatka peninsula, the Aleutian Ridge and the Immediately adjacent Pacific sea-floor. 2. To evaluate, if possible, the validity or ap plicability of the currently considered models for motion of the Pacific plate, the American plate and the Eurasian plate where they meet in the North Pacific. 3. To examine deformation and structure in sur- ficial sediments and rocks (Layer 1, especially), to the extent they can be penetrated with high powered seismic reflection profiling systems, for evidence supporting or negating subduction of oceanic crust. Figure 3. Generalized chart of the North Pacific Ocean showing Kamchatka, the Aleutian Chain, and the area of study. 14 15 7 0 ° Arctic 130° Gulf of Aioaka AREA STUDY 0 500KM t l i i ij 150° 160° 170° 180° 170° 160° 16 4. To seek evidence* ocher chan seismic evidence* co supporc or negate Che idea of transform relationships along the Pacific place-wesCem Aleutian boundary. 5. To examine Che daca for any evidence bearing on the position of the boundary between the North American and Che Eurasian places. Acknowledgment s I would like especially to acknowledge the long term encouragement and interest of my colleagues* David W. Scholl of the U. S. Geological Survey and Edwin L. Hamilton of the Naval Undersea Center. The manuscript was significantly improved as a result of long* stimulating discussions and arguments with them and their critical re view of the final draft. David G. Moore of the Naval Undersea Center and Michael Marlow of the U. S. Geologi cal Survey have read all or parts of the manuscript. Their suggestions for improvement are gratefully acknow ledged. Early discussions of the Aleutian trench with Roland von Huene of the U. S. Geological Survey were in fluential in deciding to undertake the project. It is a pleasure to acknowledge the assistance* advice and critical review of my thesis committee at the University of Southern California* especially Drs. G. A. Davis* D. S. Gorsline, and R. 0. Stone. My employer, the U. S. Naval Undersea Center* 17 generously provided technical and photographic assistance in the preparation of the manuscript and permitted ab sence, under the Graduate Academic Program, from my regu lar duties to attend classes during the two-year period 1968-1970, Employment at the Center, also, made it pos sible to participate as a leader of the 1970 Bering Sea Expedition, an undertaking which provided the necessary data for this thesis. The skill of Capt. Paul Wade and the crew of USNS JOHN D. BARTLETT in navigation and over-the- side sampling is acknowledged with thanks. The forebearance and help of long-suffering wives is always a necessary acknowledgment in the writing of any dissertation. Margaret G. Buffington is no exception. Multiple drafts of the manuscript were typed, re typed, and typed again by Edna May Helnlein, whose uncom plaining help it is a special pleasure to acknowledge. FIELD MEASUREMENTS AT SEA Aleutlan-Bering Sea Expedition of 1970 The data which constitutes the new field evidence on which this dissertation is based were collected on one segment of a cooperative oceanographic expedition between the U. S. Navy Undersea Research and Developnent Center and the U. S. Geological Survey during a 3-month period In summer 1970. The expedition was fielded aboard USNS JOHN D. BARTLETT (T-AGOR 13), an oceanographic research vessel operated by the U. S. Navy Oceanographic Office. With a mixture of military, oceanographic, economic, and general ly scientific objectives the expedition was organized into five legs as followsi Leg 1 - Along the Pacific coast - San Diego to Port Angeles, Washington. Leg 2 - Across the Gulf of Alaska to Adak. Leg 3 - From Adak, west along the Pacific side of the Aleutian Chain to Kamchatka, north to Karaginski Island in the Bering Sea and return to Adak via the Shirshov Ridge and Bowers Basin. Leg 4 - From Adak northwest across the Bowers Basin to Cape Olyutorski on the Siberian Coast, northeast to Cape Navarln, southeast along the continental margin of North America In the Bering Sea, through the Aleutian Chain at Seguam Pass and terminat ing in Kodiak Island. 18 19 Leg 5 - Return from Kodiak Island to the continental United States. Legs 3 and 4 of the expedition* which lasted from 6 August 1970 until 25 September 1970* were organized into 120 lines* each line constituting a traverse by the ship where course and speed remained fairly constant with out major change. Lines 30 to 48 in Leg 3 cover the area discussed in this dissertation. Their combined length is approximately 2500 km (see Table 1* PI. 1). The purpose of identifying each line as described below was to facilitate identification and location of seismic and magnetic data* samples* and special measurements such as wide angle reflection work with radio-sonobuoys. Further* this systematic approach permitted the easy codifying of satellite navigation position data for later print-out of the track by computer. Thus, B-30-C-1 Identifies (C)ore number (1) taken on (B)ARTLETT cruise line (30). The same nomenclature with (S) stands for sonobuoy and (D) for dredgehaul. Approximately 12 scientists and techni cians worked on a 24-hour basis for the 8 week period covered by the two legs to obtain the data. Measurements and Sampling Continuous Seismic Reflection Profiling By far the most important geophysical measurements were made with continuous seismic reflection profiling 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 20 Distances of individual lines (graphically measured from computer plot of track on Chase and others (1970) chart Nautical Miles fx 1.0) Statute Miles (x 1.15) Kilometers (x 1.85) 193.00 222.00 357.00 82.00 94.30 151.70 18.00 20.70 33.30 16.00 18.40 29.60 8.00 9.20 14.80 51.00 58.70 94.40 121.00 139.20 223.90 128.00 147.20 236.80 75,00 86.30 138.80 4.50 5.20 8.30 5.00 5.75 9.25 8,00 9.20 14.80 11.00 12.65 20.35 153.00 176,00 283.00 138.00 158.70 255.30 123.00 141.50 227.60 77.00 88.60 142.50 96.00 110.40 177.60 55.00 63.25 101.80 1362.50 1566.78 2520.50 21 equipment. This type of equipment Is a post World War 11 development, first utilized In petroleum exploration In the 50*s (McClure and others, 1958) and later evolving Into a powerful research tool employing a wide variety of energy sources. Seismic reflection profiling systems now utilize pneumatic (air gun), spark, and gas explosion energy sources in addition to the magneto-strictive or plezo-electrlc transducer types used In the more primitive, earlier, low powered systems. The principles and tech niques of seismic reflection profiling are discussed In detail by Moore (1969), who also described the determina tion of sound velocity In subbottom layers by wide-angle reflection methods. Such measurements are useful in both determining the true thickness of layers (especially sedi mentary ones) and In providing a basis for estimation of rock type. Wide-angle reflection measurements utilize an expendable radio-sonobuoy which telemeters the echo return to the ship as it steams away, rather than receiv ing them through the towed hydrophone streamer. Sonobuoy measurements were made cm several occasions during the expedition. The seismic reflection profiling system used aboard the BARTLETT to collect the data used in this dissertation had a maximum energy output of 160 kiloJoules (kj) dis charged synchronously through four spark electrodes 22 trailed from the fantail of the BARTLETT, two to port and two to starboard. Signals were received through two Teledyne preamplified hydrophone streamers, also trailed from the fan-tall approximately 100 m behind the ship* The signals were processed through Geospace Model 111 amplifiers also containing band pass filters, most common ly set between 20 Hz and 72 Hz. Magnetic Measurements Measurements of absolute strength of the earth's magnetic field were made by trailing a Varian proton pre cession magnetometer behind the ship. The information was continually recorded on analog equipment. In addi tion, direct readings were made and logged each half hour as back-up. An attempt to digitally record this data was unsuccessful. A summary of successfully retrieved mag netic data is given in Table 2. The track for the NUC-USGS 1970 expedition was pre determined based on prediction of areas which would pro vide the best information on the objectives defined. Ex amination of seismic records, as they developed, provided the basis for some alterations of the pre-determined course in order to improve the quality of the deta, or to respond to some opportunity which appeared to be developing. 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 23 Zulu Ilffifi 2210 0600 0815 0955 1105 1630 0450 1655 1400 1630 0900 0700 1930 1600 2202 Magnetic anomaly profile tabulation FROM TO Julian Zulu Julian Qax_______ lias_______ QSX___ 224 1735 225 225 2215 226 226 0630 226 226 0820 226 226 1000 226 226 1110 226 226 1800 227 227 0450 227 227 1735 228 228 2230 229 229 1700 230 230 0930 231 231 1141 231 231 2000 232 232 1630 232 24 A computer-controlled precise navigation system which received its position data from polar-orbiting navigational satellites was utilized aboard the BARTLETT. The functioning of this system has been described by Buf fington and Bachman (1972) and the accuracies developed in the Aleutian area have been reported by Buffington and others (1970). A good satellite fix, on the average, is dependable within 0,1 nautical mile (600 ft). Lines 30 through 48 are controlled by 166 of these fixes, abetted by radar fixes when close to shore and by Loran A fixes when available. With the exception of a brief period on Line 44, when the satellite navigation system was in operable and only dead reckoning and poor Loran A could be employed, positions were controlled or checked by satellite fixes. Thus, on the average, absolute position accuracies are good to 600-1000 feet. All possible types of positioning scheme combina tions were utilized and evaluated against the satellite fixes as a reference. When tracks thus controlled are plotted on the best available bathymetric charts avail able (Chase and others, 1970), correlations between local topography and geomorphology and structure as revealed from the seismic profile are much more significant. Dredging 25 Although ambitious plans for deep dredging on the steep walls of the trenches were made, dredging was limited by the length of wire available on the ship's Intermediate winch after the deep-sea winch became in operable. Considering that a 2»1 scope Is almost manda tory for successful retrieval of hard bedrock in dredging* the lower limit of this sampling technique was approxi mately 2500 m below sea level. Dredging attempts below these depths returned only surficial sediment or soft bed rock. never hard bedrock. Dredge hauls are indicated by breaks in the seismic records and are labeled. Position on the chart (PI. 1) can be identified by using line number and Zulu (Greenwich) time. The contents of the hauls are listed in Appendix C. All dredging was ac complished with chain-bag dredges, some with woven cotton cord interliners. The large number of lost dredges at test to the rugged, hard-rock topography encountered at many places. Coring Piston coring was included on the sampling program, but results are not particularly significant. Time pre cluded repetitive efforts in the face of scheduled higher priority seismic measurements. REDUCTION OF DATA ASHORE Seismic Reflection Records Original seismic reflection profiling records for the 2520 km of ship's track were put into manageable for mat aa followst 1. Photographic copies of segments of the original 46 cm-wide (18% in) records were made on high- contrast black and white 10.2 x 12.7 cm (4" x 5") polaroid film. This accomplished approximately a 28 X reduction. Overlap of about 50 percent was incurred to minimize error caused by spherical abberation in the photography. 2. A precise vertical grid, to the scale of the reduced photography, and encompassing the entire water column and maximum depth of penetration of the seismic energy, was drawn on white Illustration board. Vertical divisions on the scale were in units of water depth (with an assumed water velocity of 1500 m/sec) and one-way travel time. Thus a 1 second time interval was equivalent to 1500 m of water depth. 1500 m would be a minimum thickness for a rock or sediment interval which had taken a second for the sound energy to penetrate (assuming it did not have a velocity less than sea water). Throughout 26 27 Che dissertation reference to sediment layer thickness Is made In terms of seconds or decimal fractions of a second* because the velocity of sound In the rock Is unknown* and true thickness can only be estimated. 3. The original records were marked with time lines every haIf*hour at a minimum and the reduced photo graphs were trimmed with a razor blade along these lines so they could be butt-joined as they were forced to con form to the grid. Where a photograph was not Initially aligned with the grid* because of spherical aberration ef fects* It was trimmed with a miter cut In that portion where the bottom and subbottom were not displayed. With the exception of Line 30 (which had to be assembled In two sections because of its length) the entire seismic re flection record for each line was assembled as a continuous "panoramic" strip mosaic. The board with the mounted photographs was then appropriately annotated with Green wich (Zulu) times* Julian dates* ship's coarse and speed* firing rate of electrodes* sweep rate of the recorder* frequencies filtered* etc. Graphic scales for horizontal distances using the most typical ship speed were added. Vertical exaggeration is a direct function of ship's speed (1.05 times ship speed)* and was commonly about 10 X as great as the ship's most comfortable cruising speed* about 9.5-10 knots (see Table 3), These photo-mosaics of thu seismic records constitute the bulk of the basic data. 28 Table 3. Vertical exaggeration on seismic profiling records (for Raytheon Precision Fathometer Recorder used on northwest Pacific-Bering Sea Expedition of 1970) Ship1 a Speed* (knots) Vertical Exaxaera t i on** 10.0 10.50 9.5 9.98 9.0 9.45 8.5 8.93 8.0 8.40 7.5 7.88 7.0 7.35 6.5 6.83 6.0 6.30 Vertical exaggeration is Independent of recorder sweep speed* and for the records in this dissertation is solely a function of ship's speed. Multiply ship's true speed (distance made good — time) by 1.05 for vertical exaggeration. 29 4. For purposes of interpretation the reduced and mounted photographic seismic records for each line were covered with a hinged flap of heavy weight Herculene, a non-dimensional mylar tracing material. This is almost transparent and all details of the seismic record could be observed through it. Interpretative lines were drawn on the mylar as the records were studied and significant lithologlc or structural elements identified. As the analysis of the data progressed and stratigraphlc units could be identified or given names, the interpretative overlay was annotated. Steep slopes were measured) structural features such as faults, slumps, folds and downwarped structural basins were so labeled. The result ing annotated overlay constitutes an interpretative structural cross-section of the geology along the line traversed. Detailed descriptions and the rationale on which the interpretations are based are included as Appendix A* These descriptions are organized by lines with a general statement preceding the notes which are keyed to the seismic data by time intervals. 5. Finally, both the reduced photographic record of the original data and the interpretative overlay were photographically reduced again to film positives of a dimension suitable for reproduction. These are presented as Plates 2 through 25. Magnetic Data 30 Field data consisted of readings of absolute magnetic field strength logged at half hour intervals, and analog tapes of continuously recorded absolute magnetic field strength (when the recorder ms working). All data were labelled with Julian dates and Greenwich (Zulu) times taken from the same chronometer used to annotate the seismic and navigational data. This permitted precise relation of the magnetic data to the seismic data and to position. In the laboratory the magnetic intensity data from ship board were fed into a computer program developed by McHendrle (1972) which reduced them to magnetic anomaly profiles, given geographic coordinates and tine. The program removes the IGRF (International Geomagnetic Re ference Field) field from the observed value, thus calculat ing residual magnetic anomalies along the track of the ship. All three values, total field intensity regional, or IGRF field, and residual anomaly are printed as an ordinate on the graphic output against time and data as the abscissa. These plots are presented as Plates 25 through 41. Magnetic profiles thus can be correlated with the reflection profiles to give some Insight as to the nature of rock along the ship's track. In their present form, the magnetic data are not sufficient for delineating 31 the reversal patterns necessary for Inferring age with regard to origin of oceanic crust at a spreading center. Navigational Data Watch was kept on the satellite navigation system on a 24 hour basis and a running plot was kept on the largest scale published bathymetric chart available, as each sheet was completed and the ship moved to an area covered by another chart, the completed segment of track was reviewed and checked by the scientists and the ship's officers. The detailed movements, or drift, of the ship while dredging or sampling were reconstructed and a final total track agreed upon. The track was annotated with Julian* dates and Greenwich (Zulu) time, with special symbols utilized for each type of position* (Most ships' navigation procedures require that all times are local times--which can create considerable confusion when there are frequent changes of time zones.) The line number, dates, times, and coordinates of all fixes and positions, all course changes, and all speed changes, were logged on key-punch work sheets for later transferral to IBM com puter cards. In the laboratory this information was * In navigational usage the days of the year may be numbered sequentially from January 1 (Julian Dey 1) to December 31 (Julian Dey 365). This is essential in read ing computerized satellite fixes. punched and then utilized in a variety of computer programs permitting precise plotting of the track on a number of different types of chart projections at any desired scale. The final computer plot for this thesis was made on a mercator projection to the scale of the Chase and others (1970) chart of the northern Pacific and Bering Sea. Hourly positions are indicated by a "tick" on the track line. Noon* midnight* and the Julian date are annotated. This plot was transferred to the bathymetric chart and is shown as Plate 1. The magnetic, seismic* and sampling data can be related directly on the basis of time and date information. BATHYMETRIC, GEOLOGIC AND TECTONIC SETTING General The area Investigated is conveniently divlsable Into three broad regions that have contrasting geologic and tectonic characteristics! although two have com parable bathymetric characteristics. These arei 1. The Western Aleutian Ridge with its adjacent terrace and trench. 2. The Kamchatka Peninsula, with its adjacent terrace and trench. 3. The area of the Pacific Basin outlined by the convergence of the Aleutian Ridge and the Kamchatka Peninsula. This includes the terminal portion of the Emperor Seamounts chain and adjacent segments of the abyssal sea-floor. The Aleutian Ridge, 2200 km in length, is a classic, curved, island arc and the Kamchatka Peninsula, at least as viewed in global perspective, is also. The intervening sea-floor is unique in that it is essentially bisected by a major seamounts chain which trends toward the Junction of the two island arcs (Frontispiece). The 33 34 trend does not Intersect the Junction of the arcs but rather curves to the west a short distance to the south* The reader also Is referred to Figure 1 of Marlow and others (1973a), a comparable physiographic diagram to the frontispiece, and which gives views of the Aleutian Ridge and Trench between longitude 171° and 175° £ and longitude 171° W. The area between longitude 171° and 175° £ is noteworthy because it shows the Near Islands (Attu, Agattu and the Semlchis) and adjacent submarine physiography where Lines B-30 and B-31, the initial survey tracks of the present study, were run. Stratigraphic Framework Prior to discussing the rocks, structure, and stratigraphy of the Western Aleutians and Kamchatka, it is convenient to note that a common thread, or pattern, of gross stratigraphic relationships has emerged* This can be used to provide a general framework of reference for describing and discussing both the offshore and onshore rocks of the Aleutian Ridge and the Kamchatka Peninsula, the sediments of the two adjacent trenches, and the con tained segment of oceanic crust. The basic elements of the pattern consist of (1) pre-Tertiary rocks, generally absent in the Aleutian Ridge, but present in different form in the Kamchatka Peninsula and the oceanic segment of the sea-floor south 35 of the trench Junction, (2) early Tertiary rocks (Pale ogene) ranging in age from Faleocene through middle Miocene and distorted to varying degree by a mild to strong mid-Miocene orogeny* Lying with recognizable un conformity in many places on the Paleogene rocks are (3) relatively undeformed upper Tertiary to Holocene (Neo gene) rocks. Quaternary volcanos (4) may provide an upper element in Kamchatka. They are lacking in the Komandorsklyes where the last volcanlsm occurred at the end of the Tertiary (Zhegalov, 1964)i rocks from dredge haul B-49, northwest of Bering Island, have given radio- metric dates of 4.65 ra.y. B.P, (Scholl and others, 1973b). In the Near Islands, Gates and others (1971) report no Holocene or historically active volcanos, in contrast to the Aleutian Islands farther to the east. This highly simplified pattern is not absolutely rigorous in all cases and is complicated by eplzonal plutonlc activity, probably of late Miocene age (10-16 m.y.). The Paleogene and early Neogene rocks of the Near Islands were referred to by Wilcox (1959) as the "Early Marine Series" (EMS). This usage was applied to all rocks in the area of study which appear to have that age either established or Inferred by stratigraphic position. The late Neogene rocks which post-date the mid-Miocene orogeny have been correspondingly called the "Late Series" by Scholl and others (1973a). They are referred to as the "Late Marine Series'* in this dissertation. Most of the rocks and rock formations recognized in the Aleutian Ridge seismic sections of this dissertation are assigned to one or the other of these two broad categories. The major portions of the recognizable section off Kamchatka also are associated, sometimes on the basis of strati graphic similarity* with the pattern. And finally* the pelagic sediments of the sea-floor south of the crench Juncture which can be dated and defined on the basis of information from JOIDES hole 192* are likewise fitted into the pattern. The general characteristics of the Early and Late Marine Series are shown in Table 4. Western Aleutian Ridge and Komandorsklyes GgngJC&I Von Huene and Shor (1969) divided the Aleutian trench into four segments* the eastern two of which are associated with the Alaskan mainland and the Alaska Peninsula. The remaining segments have been labeled the Central and Western Aleutian Trench Segments respectively. According to these authors* the Central Aleutian Trench parallels the Aleutian Ridge from Unimak Pass* at the end of the Alaska Peninsula, to longitude 180°* whereas the western trench segment extends from longitude 180° 37 Table 4. Characteristics of Early and Late Marine Series, Western Aleutian Ridge (Gates and Gibson, 1956; Wilcox, 1959; Marlow and others, 1973a; Cameron and Stone, 1970; Scholl and others, 1973a) Early Marine Series Late Marine Series (EMS) ?LMS) Predominantly marine volcanic and sedimentary sequences. Complex volcanic rocks; subaerial sedimentary and volcanic sequen ces; gently dipping or flat-lying except for Quaternary strato- volcanoes and water-laid (marine) facl**~ Interbedded marine lavas (spillltes and keratophyres), tuff breccias, thinly bedded cherts and cherty argillites, limy gray- wacke, tuffaceous sandstones, siliceous and cherty slate. Spillltes altered by low temper* ature, late*stage solutions which affected labradorite but not auglte. Volcanic Rocks - basalt to rhyo- lite, andesite predominates. Volcaniclastic sediments; Inter bedded lavas. Spillltes Ho Spillltes Synorogenic plutonic rocks; gabbro to granite; diorlte and grano- dlorite predominate. Ho Intrusive Igneous equivalent known. Rocks of EMS intruded by plutons of intermediate composition; this accompanied by high intensity alteration. Includes Quaternary strato- volcanoes on those Islands where they exist (central and eastern Aleutians). Upper Ollgocene pyroclastics, cffuslves, tuff breccias and conglomerates of the Cape Tol stoy Formation In the Kcman- dorskiyes; also pelltes, pssmmites and cooglosMratas of Lower Miocene Buyanov For- swtlon In the Komandorskiyes (Zhegalov, 1964), Possibly silts, politic tuffs, and psaassltic tuffs of Upper Miocene (7) Kamenskiy Formation* includes andesites and interbed- dad breccias of Watershed Forma tion (Pliocene) on the Koamndor- sklyes (Zhegalov, 1964). Kamenskiy Formation questionably IMS; could be EMS on basis of angular unconformity on top. Pre- and synorogenic with the middle to late Miocene orogeny. Post orogenic to the middle-late Miocene orogeny. Early MaTlne Series 38 Late Marine Series Change from submarine to sub- aerial volcanlsn accompanied up lift during the Miocene. Possibly late Cretaceous, Paleo gene and early Neogene Late Neogene Equivalent to Early Marine Series of Wilcox <1959) and Early and Middle Series of Scholl and others (1973a). Equivalent of Early Series of Marlow and others (1973a). Equivalent to Late Series of Marlow and others (1973a). Equivalent to Late Series of Scholl and others (1973a). Base of EMS poorly known; not well exposed. Typically unconformable on EMS. Type section In Near Islands. No specific type section. Data from a number of sources. Terrestrial to bathyal environ ment (marine and non-marine). Both marine and non-marine en vironment of emplacement or deposition. Possibly geosynclinal type de position ( sateron and Stone, 1970). Possibly deposition in iso lated, perched intra-ridge basins; (Scholl and others, 1970a). Deposition of LMS in trenches, isolated basins, etc. during Neogene is possible corollary to EMS deposition. Today is a possible analogue to depositlonal conditions. Widespread alteration of rocks. Lack of widespread alteration. Rapid facies changes, local un conformities, pens-con tesq>or- aneous deformation. Rocks substantially deformed. Little significant deformation. 39 paralleling the Ridge Just past the Komandorskiye Is lands where it, to all intents and purposes, Intersects the Kuril-Kamchatka Trench. Marlow and others (1973a) considered the Central Aleutians to cover the region be tween longitude 171° E and longitude 171° W. In the present paper the exploratory track starts at about longitude 175° E (slightly overlapping the area of Marlow and others, 1973a) and ends beyond the Komandorskiyes and the terminal bathymetric vestiges of the arc off Cape Kamchatskly. This is considered to be the Western Aleutians. When speaking of the Western Aleutians generally, the Trench and Ridge are not considered separately in any geographic connotation. There do not exist for the Western Aleutians the same magnificently detailed bathymetric charts which have been prepared for the Eastern Aleutians and part of the Central by Nichols and Perry (1966). These charts end at the United States-Russla Convention-of-1867 boundary. The westernmost of the six-chart series, which includes the Near Islands, shows only the ridge and the northern slope of the trench, not the trench Itself. The remainder of the ridge and trench and the bathymetry south of the trench in the Western Aleutians is best shown in the chart by Chase and others (1970) (PI. 1). This chart is modem, and as accurate as the available data through 1970 permit (T. E. Chase, personal communication) but it does not have 40 the detail of the Nichols and Perry charts. Major physio graphic features are discernible, however. Exposed Western Aleutian Ridge The subaerlally exposed land area of the western Aleutian Ridge comprises two Island groups* the Near and the Komandorskiyes. The Near Islands, a part of the United States, consist of Attu, Agattu, Shemya, AlaId and Nlzki Islands, the latter three collectively known as the Semichi Islands. The total land area of the Near Is lands (Gates and others, 1971) Is about 919 sq. km (355 sq• mi•)■ The Komandorskiyes, at the westernmost portion of the Ridge, belong to the Soviet Union and consist of two fairly large islands, Bering and Mednl (sometimes spelled Mednyy by the Soviets). Together they have about 1420 sq. km (548 sq. mi.) of exposed land (Zhegalov, 1964). The easternmost portion of the Komandorsklyes is approximately 573 km (310 nautical miles) distant from the westernmost portion of the Near Islands. The westernmost portion of Bering Island is only 185 km from Cape Kam- chatskly on the Kamchatka peninsula. While both the is land groups are surrounded by relatively broad Insular shelves to depths of 1097 m (100 fathoms), the eastern half of the submerged intervening area of the ridge has an almost chaotically patterned topography with both shallow- 41 ly and deeply submerged peaks* transecting canyons* and totally enclosed depressions (Chase and others* 1970). This segment corresponds almost exactly with the southward projection of the north*south trending Shlrshov Ridge which divides the Bering Sea Into two deep basins. The western half of the submerged ridge area between the two Island groups Is heavily Incised with submarine canyons also* from both the southwest and the northeast but the general aspect of the topography Is not so Irregular. Exposed rocks of the Central Aleutians and the Near Islands have been described and discussed In differ ing detail by Sharp (1946)* Gates and Gibson (1956)* Coats (1956, 1962), Wilcox (1959), Anderson (1970), Scholl and others (1973a), Gates and others (1971), Scholl and others (1970a), and Marlow and others (1973a). Informa tion on the geology and rocks of the Komandorsklyes Is scant except for the work of Zhegalov (1964) which Is In cluded In a comprehensive work on the Geology of the USSR, fortunately available In an &igllsh translation. The work of other Russians in the area Is extensively cited by Zhegalov. Koaandorsklve Islands The first modem and relatively systematic geologic exploration of the Komandorsklyes appears to have been made by Morozevlch In 1903 with results published In 42 1912. Morozevich (as discussed in Zhegalov* 1964* p. 696) considered Che islands to consist of "eruptive and sedimentary-tuffogenous rocks of the Tertiary Period," the tuffogenous pyroclastics being primarily pelites and psammltes. Zhegalov (1964) subdivided the Paleogene-Neogene (Tertiary) rocks of the Komandorsklyes into four forma tions (or "stratums" as he calls them)* with no mention of any underlying basement of greater age. A general summary of the stratigraphic relations is shown in Table 5. Quaternary volcanoes which mark the eastern and part of the central portion of the Aleutian Ridge are notably lack ing. The only Quaternary deposits are organic lake-swamp sediments and "eluvial-deluvial" deposits covering older rocks in a thin* friable film. Zhegalov (1964) considered these deposits of little significance and attributed the general lack of Quaternary deposits to late Quaternary (Holocene 7) uplift of the Islands and consequent erosion. The basic* single* continuous structure of the islands is that of a major anticline with the axis trend ing northwesterly. On Mednl Island the limbs of the anti cline have dlpa of 35° to 40° which Increase to 70° or 80° near some transecting faults with northeast strikes. Dis placements on these faults are not known* although at least 1000 m of section is repeated in one location. The age of the faulting is Quaternary. On Bering Island the 43 Tabic 5. Sumry of stratigraphy of the Komandorskiye Islands (Zhegalov, 1964) FORMATION NAME LOCATION LITHOLOCY AGE No significant deposits Mednl and Bering Swamp deposits; friable deposits < 1 m thick Quaternary m « s —4 Vi £ V 4 J 3 WATERFALL STRATUM (WATERSHED STRATUM) (Formation ?) Mednl Island only Effusives, ande- sites and andesltic tuffs; interbedded breccias (max. 500 m) Pliocene (probably). No fossils. Youngest Tertiary in Koaandor- skiyea. to H M g CO e AflUUL KAMENSKIY STRATUM (STONE STRATUM ?) (Formation ?) JiR UNCONJ Bering Island Slltstone, pelitic tuffs, psamnltic tuffs; tuffogenous massive diatomlte and tuffo-diatom- ites are character istic « 1100 m Upper Miocene(not younger) Youngest rocks on Bering Is. Contain diatoms. w V —4 f r * 8 «m4 u 2 —4 M *3 BUYANOV STRATUM (Formation ?) Mednl Is. Bering Is. riONAL Conglomerate with exotics, pelites (mudstone)f and psammites (fine grained, fissile clayey sandstone) 200-400 m Lower Miocene ( from fossils) CAPE TOLSTOY STRATUM (Formation ?) South and Central parts of both Ber ing and Mednl Is. Conglomerate, pyroclastics (psamnltic and psephitlc tuffs), effusives and tuff breccias; ac cumulated In an environment of intense volume and tectonic activity. (Sad. tuffogenous = 2800 m Effusives - 1500 m Upper Oligocene ( from fossils) 44 faulting is apparently less intense* but is still re flected in the topography* In addition, the anticlinal axis undulates in the middle of the island to form a major synclinal depression. Indications of a synclinal struc ture are evident in the subbottom reflection profiles on Leg 48 (PI, 24 and 25) which are in approximately the right position to be a seaward extension of the Bering Is land syncline. Zhegalov (l964) remarked on the presence of late Tertiary (?) voleanIsm (effusives of the Waterfall "stratum") on Mednl, and its absence on Bering Island, without suggesting any implication. The most important orogenic activity in the Komandorskiyee occurred in the late Miocene and deformed the Commander Series which comprises the lower three of the formations shown in Table 5. This deformatlonal event is marked by angular unconformity and provides the basis for relegating the Commander Series to the "Early Marine Series" and the Waterfall formation to the "Late Marine Series•” The entire section in the Komandorsklyes has a total thickness of about 5000 m with at least half of that comprising the Upper Oligocene Cape Tolstoy formation Stratum. According to Zhegalov (i964) the Oligocene rocks were deposited in a shallow water basin accompanied by tectonic activity and active volcanlsm. The tuffaceous 45 rocks are andesitic, as are the lavas on Mednl Island. The overlying Buyanov Formation is relatively thin (200-400 m) but is alleged to represent the period marking the end of the Paleogene and the beginning of the Neogene. Its conglomerates may indicate tectonlsm In the form of uplifti and perhaps also minor folding. The so-called "Kuril” folding was widespread In the nearby Kuril- Kamchatka arc during the same time interval. Following deposition of the Buyanov conglomerates* the Komandorsklyes were relatively quiescent with the ac cumulation of diatomite in shallow basins and pyroclastics from distant volcanic sources. This accumulation resulted in the Kamenskiy Formation and was interrupted by strong late-Miocene folding and uplift. This orogeny is cor relative with the "Aleutian” orogeny which is typified by strong folding in the Kuril-Kamchatka arc. Folded struc tures observable on Bering and Mednl Island today were formed during this orogeny. The final late Tertiary event was volcanism re- 46 suiting in andesitic dikes on Medni Island only. 1 The trend of these dikes is such that it is possible to as sume control, or at least strong influence, by the north westerly strike of the late Miocene folding. Additional uplift, indicated by a number of sea terraces (benches), took place in the Quaternary as did the transverse fault ing. Russian geologists, in common with American geologists, have no reservations about the Komandorskiyes being situated on a common arc structure with the Aleutian Islands, the radius of this arc being about 1400 km. An overall strong genetic link is likewise acknowledged. Udintsev (1955a) carries this thought even further by sug gesting that the Komandorskiyes may be joined to Kamchatka by "underwater protuberances which seem like the remains of 2 a connection or bridge . . .H This abets several observa tions by Zhegalov (l964) to the effect that the Koaandor- A1though the Russians have not noted any late Tertiary effusives from Bering Island, dredge haul B-49- D-1, made just northwest of Bering Island in 1800 a of water, nettled several specimens of vesicular augite (ankeramlte) basalt, K-Ar dates on these specimens indi cate an age of 4.6 7 1.0 m.y. (Scholl and others, 1973b). This places the rocks in the early Pliocene on the time scale of Berggren (1972) and is consistent with the age assigned to the effusive andesltes reported from Medni Is land by Zhegalov (1964). Quote found in Zhegalov (1964, p. 720). 47 sklyes and eastern Kamchatka have "identical . • . sedi mentary deposits and magmatic rocks. . . . common fauna and flora," and the notion of Vasil*yev (1957) that the Komandorskiyes originally were attached to Kamchatka and separated from them at the end of the Pleistocene and the beginning of the Holocene. Intrusive rocks in the Koman dorski yes are represented solely by one area of quartz diorite on Mednl Island. They are reported by Zhegalov (1964) to belong to the same phase of magmatism as the andesltes associated with the Waterfall Formation of Pliocene age. This Medni intrusive body is correlated with Intrusions in adjacent areas of Kamchatka on the basis of similar chemical, textural and petrologic characteristics as well as age. Zhegalov (1964) extends his comparison of the "raagmatic" rocks of the Komandor skiyes to the entire Pacific Coast of North America and feels that this confirms the existence of a "very large Pacific Ocean Tertiary geosyncllne." The concept that the Aleutian arc is a major geo- synclinal area which encompasses part of Kamchatka is at variance with the interpretations of most other students of island arc geology. What is significant is the strong and apparently well-established affinity which the rocks of the Komandorsklyes have for the rocks of Kamchatka. This suggests the absence of any major structural or plate boundaries between the two areas in Pliocene time. 48 Wear Islands The Near Islands, Attu, Agattu, and the Semlchls (called the Blizhnyy Islands by the Russians) along with most of the other Islands of the Aleutian chain (with the possible exception of Adak and Anchltka) have not been studied In any great detail. Even though Attu was the site of military activity during World War II, when some roads and other facilities were constructed. It Is still an extremely difficult place to map and the field season Is restricted. The present day use of Shemya, as a base for orient bound United States air traffic, considerably enhanced the ease of work on this small Island. Information on the various aspects of the geology, geomorphology, petrology, and submarine topography of the Near Islands were published by Kondo (1931), Capps (1934), Sharp (1946), Scruton (1953), Gates and Gibson (1956), Coats (1956), Wilcox (1959), Zhegalov (1964), Cameron and Stone (1970), Gates and others (1971), and Marlow and others (1973a). The most comprehensive of these studies Is that of Gates and others (1971). All the Islands, although predominantly composed of lavas, volcanic ejecta, and the sediments and rocks derived from them, do not show constructional landforms, nor do they have any volcanoes (Wilcox, 1959). The near est active volcano Is Buldlr Island about 278 km to the east. The stratigraphy Is complicated and vague, and the 49 paucity of fosslliferous material makes dating difficult and imprecise at best. An attempt to summarize the stratigraphy of the Near Islands is presented in Table 6 . The most significant element in the geology and stratigraphy of the Near Islands is the widespread evidence for the middle to late Miocene orogeny which extends es sentially over the entire Aleutian Arc (Anderson, 1970i Stonei 1968r Gates and others, 1954i Fraser and Barnett* 1959| Burk, 1965). This orogeny is marked by synchronous eplzonal plutonism over a broad segment of the Aleutian arc (Anderson, 1970) and uplift and emergence of the Aleutian Ridge. Fre-orogenic rocks are characterized by the fact that they were predominantly emplaced in a sub marine environ and suffered deformation during this Miocene event whereas post or synorogenic deposits, intru sions, and flows show little to no sign of deformation. Evidence indicates that a significant portion of the post- orogenic rocks on the islands were emplaced in a sub- aerial environment. As mentioned earlier, Wilcox (1959) coined the term "Early Marine Series" for the preorogenic rocks based on a study of the rocks of the Near Islands, but neglected to name, either formally or Informally, the younger rocks. These are referred to as the "Late Series" by Marlow and others (1973a) and by Scholl and others (1973a). This nomenclature is occasioned by the pre dominance of non-marine deposits of postorogenic age on 50 Table 6, Suanary of stratigraphy of the Near Islands (Wilcox, 1959; Cates and others, 1971; Cameron and Stone, 1970) FORMATION NAME LOCATION LITH0L0CY AGE - Agattu Alluvium and beach deposits* Quaternary ' AttU Valley-fill alluvium, glacial fill, beach deposits, alluvial fan deposits, outwash trains* Holocene- Plelstocene * AttU Andes!te and daclte dikes of Chirikof Point Late Tert. or early Pleistocene Vi 04 M a w Faneto Formation Attu Red conglomerate and sands; subaerlal elastics Late Tert. early Plels. M B Massacre Bay Formation; <152 m thick) Attu Stream gravels, vol. mudflows, basaltic and andesitic lavas, pyroclastics. Late Tert. or early Plels. M s - Agattu Daclte porphry intrusion Late Tert. Shemya Underwater eruption of an desitic and basaltic tuffs; basalt plugs intrude tuffs. Post mld- Tert. MID-TERTIARY OROGENY - Extensive faulting (normal and strike slip); W, E, NE, and NW trends; uplift; formation of fault blocks. Attu Agattu Cabbro, tholelltic diabase, dikes, sills, small plutons; albite granite and keratophy- rlc dikes* Intrudes baseamnt rx., Chunlsak, Chirikof and Kruglol Formations. Kid-Tertiary (Miocene?) u Shemya Argil11tic, tuffaceous and conglOBMratlc rx. Original sedisMnts deposited in mar ine environment. Kid-Tertiary (equlv, to Chunlsak) u w a u u B Chlrkof For mation ( 61 m thick) Attu Crave1, carb. sandstone and slltstone; may be equivalent to Chunlksak and Nevldiskov Formations in age. Kld-Tert. (Miocene (?) Chunlsak Formation (610 m thick) Attu Bedded argillite, chert, lime stone, and pebble con- glomerate. Gradational Contact 51 FORMATION NAME LOCATION LITHOLOCY ACE to H Navidiskov Formation (305 m thick) Attu Marine gravels, grayvacke and conglomerate. Middle Tert, Miocene (?) UNCONFORMITY ON ATTU UPLIFT, DEFORMATION AND SUBAERIAL EROSION Kruglot Formation (2255' thick) Agattu Heterogeneous sequence-bedded argillite, siltstone chert; basaltic lavas and spllllte; tuff and tuff agglomerate, conglomerate. Equivalent to Andrew Lake Formation Adak (D, W, Scholl, pars, comm.) which is Eocene in age. Eocene (7) Undifferent iated base ment Agattu Lava, tuff, tuff agglomerate, conglomerate, argillite silt- stone and chert. (Equiv. to Finger Bay Volcanics of Adak (D. W. Scholl, pers. comm.) Late Meso zoic (Cret. or early Tertiary to £ H 5 3 Attu Albite granite, diabase, gabbro; oldest Intrusive rocks of the region. Late Meso zoic or Early Ter tiary Undifferent iated base ment prob. 3000-4500 m thick Attu Fine-grained, banded sed. rx., coarse and conglomeratic sed. rx.; basaltic, spillitlc and keratophyrlc lavas and tuff. Oldest rx. of Near Islands. Deposited in a tectonically and volcanically active marine environment; detritus not from a continental source Late Meso zoic (Cret.] or early Tertiary 52 the islands themselves. However, because the basic rela tionship of pre and postorogenic emplacement Is carried seaward, thus permitting water-deposited material to strongly predominate in the postorogenic period, the name "Late Marine Series" is considered appropriate and is used in this paper. Scholl and others (1973a) recognize addi tionally, a middle or synorogenic series that comprise plutonic bodies, comagmatic eruptive rocks, and associated sedimentary beds* Rocks of the Middle Series are middle and late Miocene in age. Marlow and others (table 1, 1973a) recognize both the Early Marine Series and Late (Marine) Series in the Central Aleutians as far east as Unalaska Island (longi tude 167° W). In addition, the Middle Series of Scholl and others (1973a) is represented by plutonlcs rocks which generally Intrude the Early Marine Series but not the Late Marine Series. Three radiometric dates on plutonic rocks give ages ranging from early to middle Miocene collected from the Central Aleutians (Marlow and others, 1973a). Submerged Western Aleutian Rldae Stone (1968) determined that only 1 percent of the Aleutian Ridge is above sea leveli moat of this is covered with tundra. These relationships combined with the general paucity of data on the submerged section explains amply why the geology and structure of the arc are so imperfectly 53 known. Still, many of the gross features of the sub merged portion can be described and discussed with some confidence. Generally* greater effort has been made in study of the central and eastern Aleutians than of the western. In the following discussion, many of the statements are based on data from the better studied portion of the arc. The general cross-section of the ridge, especially in the region of the Near and the Adreanof Islands (Fig. 2 ) is asymmetrical, with the north slope being steeper and more linear. The gradient is 263.2 m per km (14.7°). This characteristic, combined with a smooth, even topo graphy, is continuous over most of the 2 2 0 0 km long arc except for an interruption at the Bowers Ridge (Fig. 2) (Cameron and Stone, 1972). Gates and Gibson (1956) con sidered this north slope to represent a "great fault scarp" or a zone of northward dipping normal faults and to constitute "a fundamental structural element of the ridge.” No dissent to this idea is known. In contrast, the south slope of the ridge is much gentler (average about 3.5°), longer, and generally Irregular. It is heavily dissected and corrugated with canyons and sea valleys over much of Its length (Nichols and Ferry, 1966). Gates and Gibson (1956) reported that, although the Aleutian Ridge is principally tectonic in origin, Its present surficlal form (except for strato-volcanoes) Is 54 primarily the result of marine and subaerial (including glacial) erosion that has taken place since the mid- Miocene orogeny. Cameron and Stone (1970) concur with this interpretation. Opinions on the basic structure of the Aleutian Ridge by Shor (1964, 1966), Schneider (1964), Ewing and others (1965), Murdock (1967) and Grow (1973) have a com mon denominator in their conclusion that the ridge rests on oceanic crust. This crust, although somewhat compli cated by faulting and a superimposed body of volcanics and volcanogenic sediments, extends northward from the north Pacific to form the crust of the dering Sea, Shor (1966) believed the ridge to be an uplifted and considerably thickened layer of oceanic crust with the Moho separating it from upper mantle (V^ - 7.6-8 .9 km/sec) at a depth of 22-24 km deep. The crust (Vn - 6 . 6-7.0 km/sec) itself, P at the axis of the ridge, forms a "root** 14 km thick and the overlying mass of uplifted and deformed volcanics and volcanogenic sediments (Vp - 3.8-5.5 km/sec) adds an addi tional thickness of 10 km. Schneider (1964) differs from Shor only in the position of the maximum "root” depth which he places considerably south of the ridge axis. Murdock (1967) reports a "root** 40 km thick under the ridge axis delimited by an upper mantle velocity of 8.4 km/sec. Murdock (1967) Interprets the Moho as sloping upward from the position of the maximum crustal "root" 55 depth to a point 45 km south of the ridge axis where it is offset by a north-dipping thrust fault. Gravity data for the ridge and trench are exceed ingly sparse. Most is for the east-central and eastern part of the arc. Peter (1966) shows free-air anomaly pro files to longitude 180° which give large minima over the trench* the largest lying northward of the trench axis. Cameron and Stone (1970) state that Bouger anomalies be come Increasingly positive toward the western end of the ridge and speculate that this is caused by a progressively greater proportion of basic volcanic to volcanogenic sedi mentary rocks. Magnetic data on the ridge is scant« but that available is summarized and discussed by Cameron and Stone (1970) who Indicate anomalies of the order of 500 gammas • or greater* with an irregular aspect which they attribute to the predominantly volcanic nature of the ridge. The trench to the south has no systematic pattern of magnetic anomalies* but the Pacific sea floor beyond that has smooth anomalies also on the order of 500 gammas (Stone* 1968). In the more easterly portion of the trench* south of Unimak Island* Elvers and others (1967) show paleomagnetic anomalies (Paleocene in age) crossing the trench on to the terrace on the south side of the ridge. Selsmically the Aleutian arc is one of the most 56 active In the world, both in number of earthquake shocks and in total amount of energy released. The concentration of hypocenters at depths between 0 and 1 0 0 km Is especial ly notable (Barazangl and Dorman, 1969) as Is the concen tration of these shallow focus earthquakes west of longi tude 180° on the arc. Stone (1968) categorically states that there are "no deep focus earthquakes at all" along the arc, a characteristic which Is In strong contrast with the Kuril-Kamchatka arc which has a substantial number of deep focus earthquakes. The deepest known hypocenter on the Aleutian arc Is 180 km (Stone, 1968). Another characteristic of the Aleutian arc Is its strong tendency to show two parallel lines of seismicity. According to Barazangl and Dorman (1969) this Is also characteristic of the trenches in the Kuril and the Tanga-Fiji area. The significance of the double line is Interpreted by Stauder (1968a) on the basis of focal mechanism solutions, to Indicate normal faulting beneath the seaward flank of the trench and thrust faulting beneath the arc. Abe (1972) made a comparable Interpretation. Volcanlsm on that part of the Aleutian arc with contemporary activity occurs chiefly on the northern portion of the ridge, although the volcanoes are centrally located at about 170° W. While there appears to be no good association of Intermediate depth hypocenters with surficial phenomena, there is a positive correlation be 57 tween volcanoes and shallow-focus hypocenters (Stone* 1968). According to Coats (1962) the line of modem volcanoes on the north margin of the ridge lie along tear faults in an overthrust plate which propagate down to the basic thrust plane to reach their source of magma. Stauder (1972) believed that the central portion of the Aleutian Ridge is selsmically active along the boundaries of independent tectonic blocks which are permanent features* and which reflect phenomena resulting from the Pacific plate underthrustlng the Aleutian arc* Aleutian Terrace The Aleutian Terrace* or bench as it is called by Gibson and Nichols (1953) and Gates and Gibson (1956), was first described by Murray (1945) in the eastern part of the arc* It extends most of the length of the ridge on the south insular slope and is found in the Western Aleutians at depths ranging roughly from 3*0-4*8 km. The terrace ranges in width from 10 to 30 km. In the eastern portion of the arc von Huene and Shor (1969) interpreted the terrace to be a series of grabens* or half-grabens, filled with sediment and tilted shoreward. According to Peter and others (1965) and Malahoff and Erickson (1969a* b) the oceanic crust under the terrace is thinner than that under the ridge crest, but thicker than that under the trench to the south. The underlying Moho dips north* 58 In contrast Schneider (1964) considered the crust under the terrace to be thicker than under the ridge crest. Grow (1973) determined by study of refraction and gravity data that a largely sedimentary section* 5-8 km thick* underlies the terrace south of Atka Island (longitude 174° W). To the west* Gates and Gibson (1956) described the terrace in terms of two topographic unitst an inner* rldge-adjacent zone of sedimentation* shallow erosion* and perhaps landsliding and slumping* and an outer zone of chaotic relief marked with cones* knolls* elliptical depressions and sea valleys. They speculated that the inner or northern margin of the terrace marks the emergence of a possible thrust zone which dips under the ridge. In the western Aleutians the terrace can be recog nized to approximately longitude 171° E* which is the western end of the Near Islands. At this longitude It loses its Identity but regains it at about longitude 169° 30* E. The terrace continues as a recognizable feature until about longitude 166° E, Immediately south of the southeast tip of Bering Island in the Komandorsklyes. Six of the seismic profiling lines reported in this dissertation cross the south insular slope of the western Aleutian Ridge (B-30, B-35* B-36, B-37* B-38 and B-48). On the chart of Chase and others (1970), the ter race can be discerned by the distribution of Isobaths where Line B-30 runs across it on a southwesterly course (FIs. 4, 5). It can likewise be recognized on Plate 1 of Nichols and Perry (1966) which shows the slope south of the Near Islands (but not the trench). The bottom profile on Line B-30 (Pis. 4, 5) does not show the terrace well* although a local reversal in slope at about 07302 (J.D. 225), which marks a general change in slope from 12° to about 5°, could be interpreted as the inner edge of the terrace on the basis of Gates and Gibson's (1956) criteria. Line B-35 (Pis. 6 , 7) depicts an excellent cross ing of the terrace between 13302 and 14302 (J.D. 226). Here the cross-section shows a sediment filled basin of somewhat deformed Late Marine Series (7). Contained with in it a body of layered sediment suggestive of channel deposits is evident. This body shows definite signs of a back rotation similar to that suggested by von Huene and Shor (1969) for the eastern Aleutian Terrace. According to D. W. Scholl (personal communication) this basin has a very good corollary in the Atka Basin where JOIDES Holes 186 and 187 were drilled on the outer lip of the Aleutian Terrace Just south of Atka Island in the Adreanofs (about longitude 174° W). Although acoustic basement was cored at both sites (the two were separated by only 2.3 km), the oldest sediment obtained was a detached block of Miocene silt within largely volcaniclastic silt of upper Miocene age. The bulk of the sediment in the 926 m penetrated by 60 Hole 186 was contributed from the ridge as hemipelagic silt and clay or sandy turbidites. Line B-36 (FIs, 8 , 9) also shows a good topo graphic expression of the Aleutian Terrace between 1800Z and 20002 (J.D. 226). As interpreted from the seismic profiling record, the terrace here comprises an Irregular platform of 9arly Marine Series rocks with little to no younger sediment cover. Two small basins are filled with Late Marine Series turbidites or basin fill, and these strata are, again, back-rotated resulting in northerly apparent dips. The two hour segment of the track (see FIs. 8 , 9) coincides nicely with flat topography on the Chase and others (1970) chart. This flat area is only about 27.8 km (15 nautical miles) distant from the terrace shown on Line B-35. The likelihood that they are the same feature is good. Line B-37 (Pis. 10, 11) crosses a broad expanse of terrace between the 13002 and 15002 (J.D. 227) positions, as plotted on the Chase and others (1970) chart. Al though complicated by a topographic high at 15152 the seg ment of the profile starting at 13002 and extending to about 15452 is easily interpretable as a terrace. Only two small stretches of the terrace have depressions con taining mentionable amounts of accumulated post-orogenic sediment of the Late Marine Series. The outer of the two is very small and filled with channel deposits as indicated 61 by flat, closely-spaced parallel reflectors. The northernmost of the two, a basin centered at 15452, has 0,1 seconds of Late Narine Series deposits clearly lying on acoustic basement. Otherwise the terrace here is ex posed acoustic basement, crenulated strata of the Early Marine Series, with essentially no overlying sediment cover. Of the six lines crossing the south insular slope of the Ridge, Line B-38 (Pis. 12, 13) depicts the terrace and contained Neogene deposits best. The terrace starts at about 18452 (J.D. 227) with the outer limit (as marked by the center of the offshore topographic and bedrock high) at 21002. Depth at the inshore limit is about 2.6 km and at the offshore limit about 2.86 km. The terrace is a topographic basin in addition to being a structural basin. An unconformity marking the boundary between the acoustic basement (EMS) and an overlying thickness of about 0.6-0.8 seconds of post-orogenlc Late Marine Series basin-fill sediments can be approximated. Reflectors with in the basin fill suggest strongly that it conforms to the original surface on which it was deposited, at least in the initial period of deposition. Perhaps both the origin al surface and the overlying sediments were both folded some time after deposition. The relations are not defini tive. The inshore margin of the terrace is marked by a series of slumps and a miniature "rise" unit or scree. 62 The lowest point on the surface of the terrace (20152) 1b filled with recent turbidite deposits (at least younger than the Late Marine Series deposits which are the primary basin fill) which, interestingly, are slightly tilted shoreward. The age of the Late Marine Series in this area is confirmed by samples of dlatomlte present in the dredge haul made at the outer edge of the terrace. Although the Isobaths on the Chase and others (1970) chart (PI. 1) give some slight indication of a "terrace” between 3 6 8 0 m ( 2 0 0 0 fathoms) and 4000 m ( 2 2 0 0 fathoms), this is not confirmed by the profile which shows nothing remotely resembling a terrace at these depths. This is a considerable distance beyond the point where the terrace appears to terminate south of the southeast tip of Bering Island. Aleutian Trench Numerous individuals have investigated the Aleutian Trench. For their articles the reader is refer red to excellent bibliographies accompanying papers by Stone (1 9 6 8), Cameron and Stone (1971), Perry (1971), and Marlow and others (1973a). As one reads these articles he gains the distinct impression that various segments of the Aleutian Trench have been studied in inverse ratio to their distance from the west coast of North America, leav ing the Western Aleutian Trench poorly known, indeed. 63 Ic was noted earlier that von Huene and Shor (1969) divided the Aleutian Trench into four segments separated by broad "transition zones. * * From east to west these segments are labeled the "mainland" segment, the "eastern" segment, the "central" segment, and the "west ern" segment* The study area for this dissertation (longitude 174°30' E to longitude 164°30' E) lies com pletely within von Huene and Shor's (1969) "western seg ment” and the average trend of the trench and ridge is approximately northwest (305° T) here. However, it is appropriate to briefly consider the trench in its en tirety before looking more closely at that portion of the western segment which has more immediate application to this investigation. Von Huene and Shor's mainland segment is in the Gulf of Alaska and extends from the longitude of Yakutat (longitude 140° W) to that of Middleton Island Just south of Prince William Sound (longitude 146° W)j the trend is linear and directed easterly to northeasterly. The trench here is broad and shallow compared to the rest of the trench, and is possibly unrelated to the remaining portion which is arcuate in form. On the Chase and others (1970) chart (NAVOCEANO, 1971) the trench is first clearly delineated by the 200 fathom (3659 m) contour although von Huene and Shor include the shallow Yakutat Sea Valley as an expression of the segment (see U. S. Coast and Geodetic 64 Survey Chart 8500). Ita axial slope la 5.4 a/km to the west. The eastern segment of the Aleutian Trench ex tends from the longitude of Middleton Island to approxi mately the longitude of Unimak Pass (longitude 164° W) where the southeast trending Bering Sea Shelf edge would intersect. This segment of the trench is arcuate (about a center near Nome), has a broad, asymmetric, V-shaped cross- section, and an axial profile which slopes slightly (1 . 6 m/km) to the southwest. Von Huene and Shor (1969) be lieved this segment of the trench to be a half-graben structure which is normally faulted at the continental slope. The trench contains pre-trench oceanic sediment and a post-trench sediment fill which lies unconformably on the oceanic sediments (von Huene and Shor, 1969). Based on the thickness of oceanic pelagic sediments ac cumulated since the trench began to fill with turbidites, the age of the trench was estimated as Pliocene. Shor (1962) reported more than 2 km of sediment fill in the trench based on seismic reflection data. This sediment is underlain by material having velocities of oceanic crust. Von Huene and Shor (1969) consider the eastern segment of the trench to be younger than the central seg ment, a conclusion which is in accord with the general thesis that trench formation occurred progressively from 65 the west to east (ZhegaXov, 1964). In the mainland and eastern segments• turbidlte deposition follows the wester ly slope of the trench floor. Von Huene and Shor (1969) suggested (1) a Pliocene age for the trench here* (2) that there was no evidence of a thrust under the con tinental slope* and (3) that the situation did not recon cile with the plate tectonic hypothesis* In a later paper* von Huene (1972), with addition al data, modified this picture. He concluded that the Benioff zone emerges in a "complex of tectonic structures across the continental margin” and that an underthrust was not only possible, but that the extent of underthrusting could be estimated without utilizing magnetic anomalies. He further concluded that the amount of possible under- thrusting could be reconciled with Atwater's (1970) model for continuous plate movement in the North Pacific during the Cenozolc (see p. 157). Another interesting outgrowth of this study is von Huene's (1972) interpretation that the trench in the eastern and mainland segments contains depressed abyssal plain turbidites (2.25 km thick) transported from the south (Alaska Abyssal Plain), which are covered by turbldlte trench fill (1.98 km thick). The north wall of the trench shows extension and downslope, slump-type* features which may cover the turbldlte trench fill in some places. The contact between the trench and the north Mil (continental slope) may take three formsi 66 (1) trench sediment-fill extending* essentially undeform ed, under the slope* (2) blocks of trench sediment raised and tilted* and (3) unresolved structures* The north wall of the slope may be steep locally, especially as it approaches the trench floor (40°)* although dips from 3° to 10° are suggested as more typical. This compares with Perry*s (1971) average slope for the north wall of 6° and a high of 12° in the same segments. The wall on the ocean side is gentle* giving the trench an asymmetrical transverse profile. This relation persists for the en tire length of the trench. The south wall is less com plicated topographically than the north wall which ex hibits an almost chaotic complex of discontinuous benches, canyons, basins* spurs and ridges (see von Huene and Shor* 1969, PI. 2). The eastern segment has a well-documented magnetic anomaly crossing the trench at longitude 162°30* W (Perry, 1971). He considered this evidence against subduction. Van Huene (1972) notes another magnetic anomaly crossing the trench north of Kodiak Seamount (longitude 149° W) but does not consider it as evidence against the Pacific plate under thrusting the North American plate. The central segment of the Aleutian Trench extends from Unimak Pass to the 180th meridian which crosses the Aleutian Ridge Just west of the Andreanof Islands. It is arcuate In form about a point off Cape Navarln on the 67 Siberian Coast. In cross-section it is described as a truncated V-shaped depression. The axial profile is des cribed as being essentially horizontal, but the Chase and others (1970) chart (NAVOCEANO, 1971) suggests a slight westerly slope. Scholl (personal communication), however, reviewed this and other charts and concluded that a re gional slope does not exist west of 172° W, This segment of the trench, together with the western segment, approxi mately parallels the Aleutian Ridgej actually there is a slight convergence westerly toward the axis of the ridge. Together they form a true island arc complex, on contrast to the eastern and mainland segments which tend to diverge from the Alaska Peninsula (the continental exten sion of the Aleutian Island Chain) as it trends easterly. The central trench is relatively narrow and is bounded on the north by an insular slope which is characterized by the well-developed Aleutian Terrace (previously discussed) and a myriad of faults, some parallel and others trans verse to the trend and island chain. Trench deposits in the central Aleutians are turbidites which Marlow and others (1973a) relegate to the Late Series (* Late Marine Series), Their age is re ported as Pleistocene or older. Perry (1970) believed that the Aleutian Terrace and Trench here are half grabens. Marlow and others (1973a) present one profile in their study interpretable 68 this way for the trench. Here the landward wall possibly is formed in part by normal faulting. Holmes and others (1972) reported what they be lieve to be direct evidence of crustal underthrusting in this area, an oceanic subbottom reflector traceable some 2-7 kras under the ridge. Marlow and others (1973b) de mur and give an alternative interpretation to the same data. The western segment of the trench, according to von Huene and Shor (1969), is arbitrarily described as extending from the 180th meridian to the Komandorskiyes. In fact, it extends beyond the Komandorskiyes rising in a slight saddle at about longitude 164°40* £ to a depth of about 5300 m (290C fathoms) and then descending along its northwesterly trend until it meets the Kuril-Kamchatka Trench at longitude 164° E. In this area the Aleutian and the Kuril-Kamchatka Trenches are not physlographlcally separable except for their diverging trends and sharp Junc ture. An examination of the bathymetry of the western Aleutian Trench (Chase and others, 1970r NAVOCEANO, 1971) reveals that its character is somewhat different from the central Aleutian Trench. For 10 degrees of longitude (170° E-180° E) the trench is narrow and has a flat bottom slightly deeper than 6949 m (3800 fathoms), but essentially without any axial slope. West of about 172° E the axial 69 slope. West of about 172° E the axial gradient begins a long jumpy ascent toward the west* rising most steeply west of about longitude 164.5° E to a shallower depth of 5303 m (2900 fathoms) west of the Komandorskiyes. Immediately to the southwest of Bering Island In the Komandorskiyes, the Aleutian Trench, heretofore rela tively narrow, widens abruptly Into a triangularly shaped basin with an apex pointed northwest and the deepest por tion ( >3600 fathoms C6583 m) but < 3800 fathoms £6949 ) close to the Aleutian wall. Zhegalov (1964) reported a maximum depth of 7037 m (3847 fathoms) In the trench off the Komandorskiyes with wall slopes sometimes reaching 30°-35°. If this sounding were corrected for sound velocity, it Is In reasonable agreement with the Chase and others (1970) chart. In the western segment of the trench all the crossings made In this Investigation except for Lines B-32 and B-48 (Pis. 6 , 7, 24, 25) show the floor to be flat and underlain by turbidites. On Lines B-36 and B-38 (Pis. 8 , 9, 12, 13), the north side of the trench floor Is marked * by a large accumulation of what Is Interpreted as oceanic pelaglcs. On Line B-38 the turbidites are evident at two levels above the trench floor separated by small mounds of pelaglcsi the upper levels probably represent ponding from some source on the ridge. On Line B-48.(Pis. 24, 25), just southwest of the 70 Komandorskiyes, the floor of the trench has completely lost its flat character and assumed a U-shaped cross- section (with a small V-shaped channel) without any sign of turbidites. This profile matches nicely the topography of the trench as shown in NAVOCEANO (1971) as the track crosses the northwest apex of the triangularly shaped basin southwest of the Komandorskiyes previously described. Line B-48 (Pis. 24, 25) also shows large masses of pelagic sediment overlying oceanic crust on the ridge-ward side of the trench suggesting that the trench formed after the pelaglcs were deposited. The general combination of bathy metry and turbldlte distribution suggests that the Korman- dorsklye Islands and slope, western Kamchatka and its continental slope, and possibly the Kamchatka Basin to the north are doubtless the source of the turbidites in the western Aleutian Trench, and that much of the turbldlte deposition occurred after the emplacement of the mass of pelaglcs (7) and, of course, after the trench formation. For the western, central, and part of the eastern segments of the trench, the south wall is relatively gentle, averaging about 3° (Perry, 1971). It descends from the Pacific Basin floor at 5486 m (3000 fathoms) to an average trench depth Just shy of 7315 m (4000 fathoms). The profile of the south wall is convex upward and in some places it has a series of steps. The trench floor is usually flat and narrow al- 71 though minor tilting can be observed on the seismic re flection profiling records (e.g., Line B-30, Pis. 4, 5). By and large, the layering of the sediment fill of the western segment of the trench, as revealed by seismic re flection profiling transects, is flat and shows only local evidence of mild distortion (e.g., Lines B-30, B-36, B-37, B-38, B-41, B-42| Pis. 4, 5, 8, 9, 10, 11, 12, 13, 14, 15). Marlow and others (1973a) document the same condition for the central Aleutian Trench. Some small faults near the south wall are reported by Ewing and others (1965), von Huene and Shor (1969) and Marlow and others, 1973a). Holmes and others (1972) suggest that sediments under the north wall of the trench near Amchitka Island are mildly distorted. As might be expected, the thinnest crust in the entire Aleutian arc is under the trench, although there appear to be some variations depending on locality and method of investigation. Peter and others (1965) pro posed that the bottom of the crust may be only 4 km be low the trench floor (10 km below sea level). This is based on free-air gravity anomaly measurements. Malahoff and Erickson (1969a,b) reported the top of the mantle to be 14 km below sea-level, based on gravity measurement abetted by seismic refraction studies. Gates and Gibson (1956) speculated that the flat trench floor Indicated a sedimentary fill, a speculation 73 Russian geologists active there, especially alame the end of World War 11. The peninsula Juts in a southerly te southwesterly direction froa eastern Siberia and is separated from the Siberian as inland by the Sea ef To the east, the peninsula is bounded by the and the Pacific Ocean with the Aleutian Are ti proximately into its center. Approximately 1200 be in length, its northern end is an istheus 100 bn wide. Styrukovich (1964) describes it as having ■ shape llhe "stone-age flint point" with a aaxlaua width of 470 he at latitude 56°10' N. The peninsula*s is a point from which the Kuril Islands westerly to the Japanese island of Hokkaido Islands and the eastern coast of Kamchatka, the adjacent Kuril-Kamchatka Trench, f tinuous arc convex toward the southeast, an area of 270,000 km^. Its eastern ooaet is especially in contrast to its western coast, and is dented with many bays which have prominent omyee. 4 the most prominent of these is Cape Kaachetekiy marks the easterly end of the Kanchatskiy Harkov and others (1969) believed that this marks a zone on Kamchatka which should be extreme western end of the Aleutian Arc. According to Vlasov (1964) and Avdalhe (1971) Kamchatka represents a young folded ana farmed primarily 72 which is now considered to be correct. In an attempt to present a unified hypothesis on the structure of the Aleutians arc, they suggested that canyons and valleys transecting the north insular slope at an angle mark zones of normal faulting which result from differential movement within an allocthonous mass of ridge material moving south and overriding the crust of the Pacific. One northward- dipping zone of thrust faulting is purported to emerge at the Aleutian Bench and a more southerly one at the Aleutian Trench. On the south side of the trench the pat tern of topography suggests "en echelon** folding or fault ing, which, in the opinion of Gates and Gibson (1956) represents "crumpling of the Pacific Ocean floor under stress from the advancing upper plate, the Aleutian Ridge." The uplift of the crest of the ridge is attributed to arching of the allocthon as it was thrust to the south. It is interesting to note how many of the basic elements of this hypothesis survive today (some with con siderable modification) and fit in with the pattern of geophysical and bathymetric Information subsequently ac quired. Kamchatka Kamchatka Peninsula The geology, structure and tectonic history of Kamchatka is known almost exclusively from the work of 73 Russian geologists active there, especially since the end of World War 11. The peninsula Juts in a southerly to southwesterly direction from eastern Siberia and is separated from the Siberian mainland by the Sea of Okhotsk. To the east, the peninsula is bounded by the Bering Sea and the Pacific Ocean with the Aleutian Arc trending ap proximately into its center. Approximately 1200 km in length, its northern end is an isthmus 100 km wide. Styrukovich (1964) describes it as having a shape like a "stone-age flint point" with a maximum width of 470 km at latitude S6°10' N. The peninsula's southern terminus is a point from which the Kuril Islands continue south westerly to the Japanese island of Hokkaido. The Kuril Islands and the eastern coast of Kamchatka, together with the adjacent Kuril-Kamchatka Trench, form a smooth con tinuous arc convex toward the southeast, Kamchatka has an area of 270,000 km • Its eastern coast is rugged, especially in contrast to its western coast, and is in dented with many bays which have prominent capes. One of the most prominent of these is Cape Kamchatskly which marks the easterly end of the Kamchatskly Peninsula. Markov and others (1969) believed that this peninsula marks a zone on Kamchatka which should be considered the extreme western end of the Aleutian Arc. According to Vlasov (1964) and Avdeiko (1971) Kamchatka represents a young folded area formed primarily 74 in the late Cretaceous and Cenozoio and Is part of a larger geosynclinal system marginal to east Asia. It is an area of active tectonlsm as demonstrated by a high level of seismicity and volcanlsmt indeed. Petrouchevsky (1962) claimed that the Kuril Islands and the eastern coast of Kamchatka are the most seismlcally active zones in the entire world. Interestingly, most of western Kam chatka. although considered by Petrouchevsky (1962) to be an area of tectonic instability, has almost no seismicity. Essentially the same applies to central Kamchatka which has few active volcanoes, many dormant volcanoes, but only weak seismicity. Structurally and topographically Kamchatka is typified by linear trends or zones which strike northeast erly. approximately parallel to the geographic spine of the peninsula. The zones are called "Main Tectonic Regions'* or "Structural Facies Zones" by Vlasov (1964). There are three of these major "Structural Facies Zones" which are further subdivided into "Tectonic Zones" (Fig. 4). Superimposed on these "Structural Facies Zones" are two zones of volcanists. The most easterly of these trends more northerly than the "Structural Facies Zones" and transects them at a low oblique anglet the other has es sentially the same northeasterly trend as the main zones. The westernmost of the three "Structural Facies Zones" Is the West Kamchatka Zone which is characterized by Figure 4. Tectonic zoning of Kamchatka (from Vlasov* 1964). 75 P ig .10 D U g rM « f th e Teetoi&e 2onlnc o f Kaaehatka. A fte r O J I^ T lv m r, V.A.TerM oljrufc, an) Y e.P .K lanov. 1 - Bew Aarlea o f ta e to n ie soneai 2 - Sound a ria a o f e tru e tu re l* f aalaa to n e e | 3 - B m n la rle e o f eif>aiT>oaed v o lc a n ic b e lta t A - Sradiiaqry v o lc a n ic b e lt) * > - V oatoatogr vo lca n ic b v ltj A - frypaaad C e n tra l Kane hatha *w p 7 - . ‘ r v iln r jr y a a a a lf) 0 - J y n c liiv o rla i 9 - 3xaj*rj-n»wi tr o 'v h a . 1 - *a a t KaaKhetka e tra e tu ra l^ fa c io a aonot I I - C e n tra l Kaaehatka ttru c tu ra l-fa c la a ■ana) 111 - Beat Ftwchatka n tn ic tu re lo fe c la a aona. 77 a primary development of sedimentary rocks. Vlasov (1964) labels this a fore-deep on the Okhotsk platform. Included in this zone are two MTectonic ZonesH of uplift and three of depression. The rocks range in age from "Paleogene- Middle Miocene" with some upper Cretaceous* through upper Miocene andPllocene to Quaternary glacial and lacustrine deposits. The various subsidiary uplifts and depressions within the zone contain undifferentiated Paleogene and Neogene rocks with some cover by Quaternary lavas. Structures in this zone are primarily gentle folds. The second major "Structural Facies Zone" is called the Central Kamchatka Zone and it is considered to be the "inner volcanic arc" of Kamchatka. It lies to the east of the first zone and comprises, as subsidiary "Tectonic Zones," two smaller anticllnoria (the Kamchatka-Koryaki and the South Kamchatka) and two median massifs (the Sredinnyy-Kamchatka and the Ganal'skiy Protrusion). The Kamchatka-Koryak1 Anticllnorium extends almost the entire length of the Kamchatka Peninsula and is almost all vol- canlcs with shield and strato-volcanoes rising from a basalt plateau. The structure is anticlinal and com plicated by horst uplifts. The South Kamchatka Anti cllnorium appears to be a structural and topographic con tinuation of the Kamchatka-Koryak1 Anticllnorium, but separated from it (at least cartographlcally - see Fig. 3) by the Sredinnyy Massif. The rocks of both antlcllnor- 78 la are primarily Neogene effusives and intrusives. The oldest rocks in Kamchatka are found in Sredin nyy Massif. They were originally thought to be pre- Carabrian, but considerable differences of opinion exist as to exact age. Vlasov (1964). for example, prefers to call them Froterozolc (?). The Sredinnyy rocks include gneis ses, crystalline schists, phyllltes and meta-volcanics• Also present are slightly metamorphosed Mesozoic sediments and effusives. The Ganal'skiy Protrusion is essentially a south easterly extension of the Sredinnyy Massif. Structurally it resembles the Sredinnyy Massif in that it comprises a fault-bounded block of elevated metamorphlc rocks* How ever, it has a larger exposure of metamorphosed effusives than the Sredinnyy Massif. Recent work by Lebedev and others (1967) suggest that the metamorphlc complexes of both the Sredinnyy Massif and the Ganal'skiy Protrusion may be Mesozoic in age. They further report major dif ferences between the two mountain ranges comprising the Sredinnyy Massif and the Ganal'skiy Protrusion. These Include different crustal thickness, aeromagnet1c character, metamorphlc facies and grade, and different plutonlc histories. The two ranges fora two metamorphlc zones separated by the central Kamchatka depression. They are called the Sredinnyy and Ganal'skiy metamorphlc zones and are considered by Lebedev and others (1967) to repre 79 sent a typical paired metamorphlc complex of the circum- Paciflc type. Such paired belts* characterized by low- pressure and high pressure metanorphlc rocks and minerals have been discussed by Miyashlro (1972) who relates the high pressure belts to the descent of a lithospheric slab into the depths of the upper mantle and the low pressure belts to thermal effects of materials ascending from a Benloff zone. The third major "Structural Facies Zone" is the East Kamchatka Zone. Its subsidiary "Tectonic Zones" comprise two "anticlinoria," three "syncllnoria" and a small massif. The most westerly of these structures (see Fig. 4) is the Central Kamchatka Trough--a large syncline containing Paleogene and Neogene sedimentary rocks In its core (some with a flyschold character). The flanks have more volcanics and tuffaceous sediments. Structures are large folds with some fractures (faults ?). The axial element of the East Kamchatka "Struc tural Facies Zone" is the East Kamchatka "anticllnorium" or East Kamchatka Tectonic Zone (Avdeiko* 1971). Topo graphically the zone Includes several mountain ranges and projects to sea in the north to include part of Karlngln- sky Island in the Bering Sea. Rocks contained within it are primarily Upper Cretaceous sedimentary rocks and sub ordinate volcanics. Structure is characterized by steep* linear* northeast-striking folds with some faults and 80 overthrusts. The northwest boundary (in part) is a steep fault and. to the southeast, upper Cretaceous rocks are thrust over the Tertiary. Vlasov (1964) labels this zone as the "outer folded arc" of the Kamchatka tectonic system. East of the East Kamchatka Anticllnorium is the East Kamchatka Trough (synclinorium) which is itself over lapped on the east by the Tyushevskiy Trough (synclinorium). The East Kamchatka Trough contains approximately 6000- 7000 m of tuffaceous flysch deposits which are severely deformed in tight, narrow, overturned folds and over- thrusts. The overturning is to the southeast. Quaternary volcanic rocks cover much of the area. The Tyushevskiy Trough is a Neogene structure (Middle and Upper Miocene and Pliocene) in tuffaceous sediments which occupies a narrow strip between the East Kamchatka Trough and the Volcanic Region of the Eastern Peninsulas. Three large peninsulas extend out from the east coast of Kamchatka (Cape Shipunskiy, Cape Kronotskiy and Cape Kamchatskly) and together form a linear tectonic zone which is anticlinal in nature. This zone is called the Volcanic Region of the Eastern Peninsulas by Vlasov (1964) and is characterized by upper Cretaceous, Paleogene and lower Miocene volcanic and plutonic Igneous rocks. The intrusives are commonly serpentenized ultrabasics. Structures are complicated with shifting trends of beds and steep to overturned folds. These rocks are the age 81 equivalents of the Early Marine Series In the Aleutian Area. The Vostochny (eastern) volcanic belt Is super imposed on the several "Tectonic Zones" of the East Kam chatka "Structural Facies Zone” and transects them ob liquely (Fig. 4). All of the 28 active volcanoes of Kam chatka and 65 Inactive volcanoes occur in this belt. The zone is parallel to the Kuril-Kamchatka Trench. Vlasov (1964) believed that Its formation Is associated with the formation of the trench. Both the active and inactive shield and strato-volcanoes lie on "extensive effusive plateaus" (plateau basalt ?) and. in the area of Cape Kam chatka! align themselves parallel to local structural trends (Vlasov, 1964). The Sredinnyy or western volcanic belt is super imposed on the boundary between the West Kamchatka and the Central Kamchatka "Structural Facies Zones." Large areas of deeply dissected plateau basalts with associated chains of extinct and partially eroded or destroyed strato and shield volcanoes characterize this province. The volcano chains trend northeasterly. Vlasov (1958) postulated that this belt is controlled by a deep fault which was associated with all the volcanic processes in central Kamchatka from Late Cretaceous to Quaternary. Thus he regards the volcanic belt as a final or penulti mate event in the formation of the great Kamchatka geo- 82 syncline. In contrast he believed that the Vostochny Belt Is genetically Independent of the Sredinnyy Belt and began to develop In the Tertiary coevally with the Kurll- Kamchatka Trench. A common thread or characteristic of the tectonics and geology of Kamchatka, which Is emphasized by a signi ficant number of Russian regional geologists (e.g., Vlasov and Klenov, 1964i Goryatchev, 1962j Andreyev, 1963) Is that the Intensity of tectonic activity, seismic ity, and volcanlsm Increases from the west to the east. Thus Vlasov and others (1964) report gentle folding In the west which progresses to Isoclinal folding with over- thrusting In the east and finally to the Kuril-Kamchatka Trench which Is the most active contemporary locale of the entire area. According to Goryatchev (1962) the present day structure of Kamchatka began In the Pliocene with the simultaneous formation of the Kuril-Kamchatka Trench by "sagging," Intense uplift In eastern Kamchatka and slow er, milder uplift In western Kamchatka. This resulted In the aligned linear structural facies and tectonic zones Just discussed. Goryatchev obviously belongs to the Russian school which espouses vertical tectonic movements to ex plain major structural features. The superimposed zones of volcanlsm In Kamchatka! along with the Kuril Islands to the south* contain 285 volcanoes of which 66 are active. The volcanoes extend only to the latitude of Cape Kamchatskiy, with the in tensity of volcanic activity increasing from south to northf at least to the point where the projection of the Aleutian Chain Intersects the peninsula at Cape Kamchat- skly (Udintsev, 1955a). In this respect the Kuril- Kamchatka Arc and Trench are occasionally compared with the Aleutian Arc with regard to dating of formation. Starting with the Kotnandorskiy Islands and moving toward the east) seismicity and intensity of volcanic activity appear to be different in the several segments of the Aleutian Arc. Although the changes are not necessarily progressive! the conclusion has nonetheless been reached that the inception of Aleutian trench formation occurred in the west with "progressive** formation toward the east where volcanlsm and tectonism are now most active. Be cause of the progressive increase of volcanlsm from south to north in the Kuril-Kamchatka region* and the abrupt cessation of volcanlsm at the latitudinal point where the Kuril-Kamchatka trench terminates, Udintaev (1955a) and others concluded that the progress of formation for the Kuril-Kamchatka Trench was like the Aleutians, toward the most active areas, i.e., from south to north. The rocks in Kamchatka comprise a total thickness 84 of 10-15|000 ra which are primarily upper Cretaceous and Cenozoic deposits. Upper Jurassic rocks are apparently also present in Kamchatka (Avdelko, 1971). All of the rocks are penetrated by various intrusives. Vlasov and Klenov (1964) commented that the widespread close as sociation of upper Cretaceous and Cenozoic rocks is a feature the Kuril-Kamchatka Arc has in common with most other eastern Asiatic island arcs. An abbreviated summary of the geological history of Kamchatka can be made by dividing the rocks and rock sequences on the peninsula into six different groups separated by five periods of tectogenesis. The informa tion is drawn primarily from Vlasov and Klenov (1964). The oldest rocks of the peninsula may be the Mesozoic metamorphics of the middle massifs although Vlasov (1964) considered them Proterozolc. The history of their formation is only now being unravelled (Lebedev and others* 1967). The first orogenic event was pre- Cenomanian (Cretaceous) in age as evidenced by upper Cretaceous (Cenomanlan-Senonian) rocks that lie with un conformity on the older formations. A late Cretaceous- early Tertiary orogeny followed this first evena and was accompanied by the intrusion of granitic rocks. The next broad event was the deposition of Paleogene and Lower Miocene rocks followed by an early Miocene tectogenesis which the Russians call the Kurilian folding. This early 85 Neogene event is neither clearly understood* nor is its part in the tectonic history of Kamchatka well establish ed. Lower Miocene and middle Miocene rocks postdate the Kurillan folding and they* in turn, were folded in a later Miocene orogeny termed the Aleutian foldings the event was accompanied by minor plutonism. The uncon formity representing this event is widely recognized in Kamchatka. Aleutian folding in Kamchatka can be cor related with the orogeny in the Aleutian area which separates the Paleogene and early Neogene Early Marine Series from the Neogene Late Marine Series. Tectonlsm at the end of the Pliocene* called the Sakhalinian phase by Vlasov and Klenov (1964). resulted in faulting and fold ing of the rocks of Kamchatka* including some of the younger Neogene rocks* and was accompanied by alkallc intrusion in West Kamchatka. Post-Pliocene tectonlsm has been primarily uplift and differential movement along faults. The present re lief of Kamchatka is the result of this activity. Some folding occurred but it was localized* It is worthwhile to reiterate Vlasov's (1964, p. 40-41) summary statement about the deposits in the East Kamchatka Structural Facies Zone because it underlines the basis for their comparison with the Early and Late Marine Series of the Aleutians. "In the Eastern zone, especially in its part adja- 86 cent to the Pacific Ocean, the Upper Cretaceous and Paleogene*Lower Miocene deposits differ little • . • Both are crumpled Into narrow steep folds, here and there overturned and complicated by overthrusts* The Younger Neogene rocks have been constructed into relatively slop ing folds . . .M Further, the general llthologlc characteristics of the Tertiary deposits of Kamchatka are similar to those of the deposits in the Aleutian area. The Paleogene of Kam chatka (Early Marine Series of the Aleutians) comprises deep and shallow water deposits, effusive basaltic pyro- clastics, and andesitic basalts. The Kamchatka Neogene (Late Marine Series of the Aleutians) includes sediments with coarse fragmental composition which contain faunal remains, dlatomltes and more siliceous volcanlcs, e.g., andesite and dacites. The early Miocene (Kurlllan) tec tonlsm of Kamchatka does not appear to be recognized in the Aleutian area, Kamchatka Terrace Three broad embayments indent the southeast coast of Kamchatka forming prominent peninsulas which extend eastward. Each embayment appears to be the site of a par tially closed submarine basin which forms a terrace-like step in the profile of the sea-floor between the Kamchatka shore and the bottom of the trench. Lines B-44 and B-45 (Pis. 16-19) crossed the central of the three embayments and Lines B-46 and B-47 (Pis. 20-23) traversed the off shore portion of the peninsula to the north of it (Cape Kronotski)• Udintsev (1954) discussed "submarine mountain ridges" off the eastern slope of Kanchatka and implied that they are equivalent to the Lesser Kuril and the sub marine Vityaz Ridges to the south. Pavlov and Yunov (1970) indicatedt also« that the eastern peninsulas of Kamchatka are in the same structural zone as the Lesser Kuril and the Vityaz Ridges. These are reasonable as sociations and most likely correlate with the offshore structural highs which can be noted at 2315Z (2*9),Line B-44 (Pis. 16 and 17) and at 00302 (231), Line B-45 (Pis. 18 and 19), Although only general bathymetric outlines of the basin are shown on the Chase and others (1970) and NAVOCEANO (1970, 1971) charts, it appears likely that this offshore ridge may be a "breached" or incompletely formed structural rampart which dams a large volume of sediment but still permits "drainage." Similar structural highs were drilled at DSDP (JOIDES) sites 186-187 along the edge of the Aleutian Terrace (Creager, Scholl and others, 1973). A fairly well developed drainage pattern appears to lead from the basin (or terrace) area off to the trench. From the lack of turbldltes in the trench, one surmises that the drainage is either ineffective or 88 recent. These "breached" basins are Illustrated nicely by Alpha and Winter (1971) (see Frontispiece) who also show lower benches on the peninsular wall of the trench be tween the basins and the trench floor. Comparable benches on the insular slopes of the Kuril Islands to the south are described by Udintaev (i955a). These are 20-30 km wide at depths of 4000 and 7500 m. Menard (1964) be lieved that the benches are similar to the Aleutian Ter race because of their ridges at the outer rim* which function as traps to prevent* or diminish* the flow of turbldltes Into the trench. An inspection of the seismic profiles from Lines B-44 and B-45 reveals that the upper basins (the outer ridge is approximately 3000 m below sea level) are* or have been, extremely effective as sediment traps. The sediment filled structural basin which com prises a significant portion of seismic profiles B-44 and B-45 Is likewise comparable to the slope basins shown on Line B-38 on the northern wall of the Aleutian Trench. Although the basin on the Aleutian wall is much smaller and the sediment fill thinner than its counterpart off the Kamchatka peninsula* the depths of the outer rim are al most identical (3000 m). This has a significance* as yet, undeterminable. In summary* the topography of the north wall of the Kuril-Kamchatka Trench off Kamchatka is dominated by three 89 large sediment-filled structural basins. These basins* together with lower benches and an Involved bathymetry* Indicate a complex structure which probably includes both downbowing and faulting. It is presumed that the basins north and south of the basin crossed by Lines B-44 and B-45 are similar* both genetically and structurally. The basis for the presump tion is gross* superficial, bathymetric resemblance, nothing morel Kuril-Kamchatka Trench Occasionally referred to as the Kuril-Kamchatka Cavity or the Kuril-Kamchatka Trough by the Russians (e.g., Zhegalov, 1964j Udintsev, 1954, 1955b), the Kuril- Kamchatka Trench is every bit as imposing a structural and physiographic feature as the Aleutian Trench. As might be expected, most currently available geomorphlc information on the Kuril-Kamchatka Trench is from Russian papers which are based on data collected on an expedition by the Russian research vessel Vitlaz. The Vitlaz made over 50 transverse crossings of the trench in Its 1953 cruise using recording echo-sounders. The bathymetric information apparently was not utilized in the construc tion of the Chase and others (1970) and the NAVOCEANO (1970* 1971) charts. Trending slightly east of north and concave to the 90 east, the Kuril-Kamchatka Trench is long (2000 km) and narrow (2 0 - 6 0 km) as measured along the 6 0 0 0 m Isobath. At the 9000 m isobath it is 550 km long and 5 km wide. Its greatest depth is 10,377 m (corrected for sound velocity) at latitude 44°17.6' N - longitude 150°30.1' E off the Kuril Islands (Udintsev, 195*0 • The trench parallels the Kamchatka coast about 180 km offshore, Intersects the Japan Trench to the Bouth and the Aleutian Trench to the north. Udintsev (1955b) des cribed the main axis of the trench as parallel with the axes of principal structural trends in Kamchatka, but with subsidiary elements having diverging trends. This rela tion also has been noted in the Aleutian Trench. Bezrukov and Udintsev (1953) proposed that the 4500 m deep canyon between the Komandorsklyes and the Kamchatka peninsula Is an extension of the trench into the Kamchatka Basin, but give no reasons for their conclusion. The extension is not warranted as it is not obvious or apparent on the Chase and others (1970) and the NAVOCEANO (1971) charts. The northern portion of the trench off Kamchatka is Bhoaler, at an average depth of about 8 0 0 0 m, than the southern part off the Kurils which averages closer to 9000 m (Udintsev, 1954). This results in an undulating, long axial profile sloping gently to the southwest. According to Udintsev (1954), the trench is V-shaped in cross section along its entire length. The upper portions of the walls of the trench have gentler slopes than the lower parts, with an overall angle of 7°. Locally, fault scarps may have slopes of 30°-45° or more. The V-shape of the trench is truncated to a certain extent, at least in the south, with a flat bottom which is very narrow. Udintsev (1954) indicated it to be 1 km wide at a depth of 9000 m and 8-10 km wide at about 8000 m depth. A crossing of the trench cm 5 May 1966 by USNS CHARLES H. DAVIS (T-AG)R-5) at latitude 5l°21' N-longitude 160°36' E showed it to have a flat bottom 6.6 km wide at a corrected depth of 7910 m (author's files). The flat bottom is composed of turbidite sediments which were 0.06 seconds thick on the seismic profile (99 m), However, at, and north of, latitude 52°50' N, the bottom of the trench is V-shaped and completely void of turbidite fill as shown by the records of Lines B-44, B-45, B-46 and B-47 (Pis. 16-23). The V-shaped cross-sectional profile is slightly asymmetric like the Aleutian Trench. Menard (1964) ap pears to be correct in his statement that if the turbid- ites were removed from the Aleutian Trench it would have a narrow trough-like profile similar to the Kuril- Kamchatka Trench. Ckn the northwest flank the trench rises 6-11,000 m to the base of mountains of the Kuril Islands and Kamchatka, On the southeast side It rises 2500-5000 a to the sea-floor of the northwest Pacific. 92 The walls of the trench have complex topography, the landward wall more so than the seaward. According to Udintsev (1954) the seaward wall has "narrow transverse canyons" and "steep longitudinal scarps" which are prob ably of tectonic origin. The landward walls of the trench, especially off Kamchatka, are described as complexly dis sected. This is immediately apparent from an inspection of the Chase and others (1970) and the NAVOCEANO (1971) charts, especially off the southeastern coast of Kamchatka, Two benches are reported on the insular slopes of the Kuril Islands by Udintsev (1955a) which are described as being 20-30 km wide at depth of 4000 m and 7500 ra. These benches are not evident on the Chase and others (1970) and NAVOCEANO (1971) charts for the trench area off Kamchatka, but they can be detected farther south in the trench, immediately east of Hokkaido. Menard (1964) compared these with the Aleutian Terrace (bench) especial ly with regard to the characteristic outer rim behind which sediment may be trapped. The crust under the Kuril-Kamchatka Trench is con sidered to be of the "intermediate" type (Solov'yev and Galnanov, 1963). In this respect it differs from con tinental crust by the absence of a "granitic layer" and from oceanic crust by an enlarged thickness (5-12 km) of 93 the sedimentary layer. The same type of "intermediate" crust is reportedly under the Bering Sea and in the Pacific Ocean near the Komandorskiyes (Solov'yev and Ga inanov, 196 3). Belyayevskiy and Rodnikov (1971) believed the trench to be a transitional zone between continents and oceans and the site of a modern geosyncllne. The adjacent island arc is purportedly related to deep faults trans ecting the entire crust and penetrating deeply into the mantle. In their classification of oceanic basins they label the Kuril-Kamchatka Trench as a "Kuril Type" basin with the following characteristics! asymmetrical struc ture , considerable length, great depth of water— decreas ing toward the Pacific Ocean, thin sediment layer (3-4 km or less), granitic layer which, if present at all, thins toward the ocean, thick basaltic layer (to 20 km or more), / and a sharp discontinuity with the Mohorovlclc discon tinuity (Moho). This* description compares roughly with A To make sense out of this description one must go to the definitions of continental and oceanic crust by Aver’yanov and others (1961). Oceanic crust has a thin (1 km) layer of sediment and a layer of basalt 3-12 km thick for a total thickness of 10-17 km including the water column. Continental crust is a 3-layered structure with a sedimentary layer, a granitic layer and a basaltic layer for a total thickness of 20-30 km. 94 that of Solov'yev and Galnanov (1963). With regard to seismic activity, the Kuril- Kamchatka Trench exhibits the familiar pattern found in other circum-Pacific trenches, especially the Aleutian, Udintsev (1955b) reported "superficial" (shallow) earth quakes on both the oceanic and terrestrial slopes of the trench and believes that these probably form scarps of considerable height (800 m) and length (500 km) which alternate with the horizontal terraces. Presumably he is referring to what he described as benches in a different paper (Udintsev, 1955a), Medium focus earthquakes occur beneath Kamchatka and "deep" focus in the area of the Okhotsk Sea, The axial direction of distribution of the "deep" focus earth quakes is parallel to that of the trench. This forms the typical Benloff zone pattern. Earthquakes which are described as "deep" appear to be at depths around 200 km (Fedotov, 1965, Fig. l)i the charts of Barazangi and Dorman (1969) show a few hypocenters as deep as 500 or 600 km. The 200 km earth quakes would be considered "intermediate" by Gilluly, Waters and Woodford (1968, p. 472) and other observers. Kuril Island Chain Brief mention of the Kuril Islands is appropriate because, while they are considerably south of the study 95 area, they are generally considered a part or a continua tion of the arc structure of Kamchatka. The inclined (Benioff) zone of earthquake foci present beneath the Kamchatka Peninsula is also present beneath the Kuril Islands to depths of approximately 210 km. It passes under the islands proper at a depth of 150-180 km (Fedotov, 1965). The slope is approximately 31°. Piskunov and Gavrilov (1970) document a sequence of volcanogenic sediments in the Kuril Islands which are divided into a Cenozoic time frame roughly comparable with Kamchatka and the western Aleutians. The two phases are (1) early to middle Miocene and (2) late Miocene to late Pliocene. The nature of the time hiatus between middle and late Miocene is not mentioned, but orogenic activity is implied. Strel'tsov (1970) discussed a divi sion of pre-Quaternary rocks of the Greater Kuril Islands into two structural stages* (1) volcanic and sedimentary rocks of Paleogene (?) to middle Miocene age, and (2) sedimentary rocks of middle Miocene to Pliocene age. The two stages are separated by an angular unconformity. These stages correlate with the Early and Late Marine Series of the Aleutian area. The bottom of the crust under the Greater Kuril Is lands is essentially flat, which means (according to Belyayevskly and Rodnikov, 1971) that the arc has no 96 roots. Under the Aleutian arcs the Moho Is deeply de pressed to form roots. Therefore, the Kurils may be in a state of isostatic Imbalance with compensation yet to take place or they may be in isostatic balance with the density of the crustal column light enough to prevent a downbow of the Mohorovicic discontinuity. This situation has a corollary in Kamchatka to the north where Pavlov and Yunov (1970) stated that the crust ranges in thickness from 24- 32 km, with the thinnest crust in the eastern peninsulas. The base of the crust dips westward to a depth of 32-33 km in central Kamchatka before rising again. This represents an isostatic imbalance between the mountains of the east ern peninsulas (no roots) and the central mountains (roots) (Pavlov and Yunov, 1970). Sea-Floor Outlined by Trench Convergence Given the 52nd parallel as a southern boundary, the convergence of the Aleutian and the Kuril-Kamchatka Trenches defines the northern boundary of a roughly trian gular, arrowhead-shaped area of sea-floor. Basically, this area comprises a broad, topographic swell ascending from approximately the 3000 fathom (5486 m) Isobath seaward of both the Aleutian and the Kuril-Kamchatka Trench to a central high near 2743 m (1600 fathoms). The latter was the V. A. Obruchev Swell by the Russians (Udintsev, 1954). Udintsev (1954) states that the Obruchev Swell rises to a depth of 2994 m below sea level. The shoalest depth on the Chase and others (1971) and NAVOCEANO (1970) charts Is 2839 ra (corrected) (1582 corrected fathoms). The sea- floor depth for J01DES 192 was 2999 m, only 5 ra more than Udinstev*s (1954) depth. Thus, the peak of the Obruchev Swell Is likely Meljl Guyot, The sea-floor area described above is unevenly split by the line of guyots and seamounts forming the northern extremity of the Emperor Seamounts chain (see Plate lj Frontispiecet Chase and others* 1970t and NAV OCEANO, 1971). To the south, the main topographic axis of the Emperor Seamounts, after trending Just west of north (35o° T) for most of its length from the Hawaiian- Eraperor Bend (Jackson and others, 1972), bends at about latitude 50° N and trends to the northwest ( 305° T) al most directly toward Cape Kronotski on the Kamchatka coast. Another ill-defined group of seamounts occupies the area between this change In trend and the point where the southern Shlrshov Ridge adjoins the Aleutian Ridge. Indeed Udintsev (1960) speculated from this that the Shirshov Ridge is a structural continuation of the The Russians object to this name. Bezrukov and Udintsev (1955) discussed the entire Seamounts chain starting at the Hawaiian Islands and named the N-S trend ing Emperors as the Northern Hawaiian Suboceanic Ridge. 98 Hawaiian-Emperor Ridge In the Bering Sea but recent work has shown that this is unlikely (Scholl and others, 1973a), This relation is also well-illustrated in the Frontis piece. From about latitude 52°30* N the Emperor Seamounts parallel the trend of the western Aleutian structure. Meiji Guyot (site of JOXDES 192) is close to the north west terminus of the chain. There appears to be no topo graphic trend heading directly into the point of inter section of the two trenches. The sea-floor west and southwest of the seamount axis is generally smooth, with the exception of a few minor highs and depressions, as it slopes off to. the southwest (Chase and others, 1970| Frontispiece). How ever, Udintsev (1954) indicated that the sea-floor on the seaward side of the Kuril-Kamchatka Trench is uplifted over a 100 km width in a low swell whose axis parallels the trench. The swell also is documented by Dietz (1954, Fig. 1), Menard (1964) and by Hanks (1971) who called it the Hokkaido Rise. A comparable rise occurs on the oceanic sea-floor seaward of the central Aleutian Trench (Menard, 1964t Hayes and Ewing, 1970% Peter and others, 1970). Hanks (1971) describes the Hokkaido Rise as having 731 m (400 fathoms) of relief above a mean ocean depth of 5486 m (3000 fathoms), and considered it to be the result of several kilobars of horizontal stress acting on the 99 Kuril oceanic lithosphere normal to the Kuril*Kamchatka Trench. The same type of stress on the Aleutian Trench is almost an order of magnitude smaller than that Hanks (1971) determined for the Kuril-Kamchatka Trench. He sug gests that this is because oceanic lithosphere can be sub ducted into the mantle under widely varying levels of tectonic stress. Lines of small volcanoest with trends normal to the trench axis, are associated with the Hokkaido Rise according to Udintsev (1955a)i Belyayevskiy (1961) indi cated that magnetic anomalies are found with a fine structure parallel to the rise, tfhether the Hokkaido Rise, or a possible northern extension of it, exists in the sea floor area immediately south of the trench con vergence is not known. The seismic reflection profiles of this study do not extend far enough seaward to either confirm or deny its presence. The converging trenches north of latitude 54°30( N outline a narrowing ridge which comes to a point at the trench Juncture and which contains an isolated topo graphic high rising to 4279 m (2340 fathoms) below sea level (NAVOCEANO, 1971). The sea-floor to the northeast of the axis of the Emperor Seamounts (Aleutian side) has a varied topo graphy. The area from the trench Juncture south to about latitude 52°30* N is almost featureless. The charts of 100 Chase and others (1970) and NAVOCEANO (1971) show smooth, widely spaced Isobaths and a gentle slope northeastward to the Aleutian Trench. Along the northern side of the smooth area northeast of the chain* the ocean floor ad jacent to the Aleutian Trench Is dotted with a large number of seamounts* some of which rise as high as 2469 m (1350 fathoms). They are Informally referred to as the Bartlett Seamounts (see Lines BOO, B-3li Pis. 4-7). Except for the Information gained from J01DES drill site 192 (which is discussed in the section entitled RESULTS), the sediments of the sea-floor immediately south of the trench juncture are poorly known. Farther to the south, J01DES drill sites 45 through 52 (Leg 6) penetrated "Layer 1" deeply enough to ascertain the presence of Mesozoic chalks, limestones, cherts and ash (Fisher and others, 1970). An interpretative chart bawed on known dates of the "basement" in the western north Pacific shows extrapolated isochrons north to the general area of the trench Juncture (Fisher and others, 1970, Fig. 1). The inferred ages are Eocene-Paleocene and younger. The basic premise on which the chart is constructed and the iso chrons drawn is that oceanic crust becomes progressively older to the west away from the East Pacific Rise. Jackson and others (1972) suggested that, although the age of the oceanic crust in the northern Emperors is unknown, there is ample general evidence to speculate that 101 It originated at mid-ocean ridges during either the Cretaceous or early Cenozoic. Drilling at JOIDES site 192 indicates that the oceanic crust in this area is older than 70 m.y. as Melji Guyot is overlain by pelagic deposits of lower Maestrichtian age (Creager and others, 1973). Shisoef Seamount* at the Junction of the Japan and the Kuril-Kamchatka Trench, is reported by Kagami and others (1964) to have yielded shallow-water Cretaceous (Aptian ?) gastropods. Ewing and others (1966) reported Lower Cretaceous (Albian) sediment from a core taken on the Shatsky Rise (east of Japan at latitude 3l°5l' N, longitude 157°20' E) at a depth of 3500 m. This core was taken in surficial sediment which was also the outcrop of an identifiable and traceable seismic reflector. Thus, the Cretaceous age was traceable over the entire rise and two hundred meters of sediment lie between the cored Cretaceous reflector and the acoustic basement. Applying known sedimentation rates for upper Eocene pelaglcs, Ewing and others (1966) speculated that the 200 m represents an additional 66 m.y., giving the basement an age of 172 m.y. B.P. (Middle Jurassic). Thus, the consensus is that the sediments of Layer 1 in the western north Pacific immediately above the acoustic basement (presumably oceanic crust formed by sea- floor spreading) are Late Mesozoic and younger, as estab lished locally by drilling at the DSDP (JOIDES) site 192. 102 Frazer and others (1972) prepared charts based on all available described surface samples In the North Pacific Ocean. A section of this chart for the trench convergence area Is reproduced as Figure 5. The sample density Is relatively sparse but, according to the author, adequate. The Aleutian Trench is shown as fine clay and terrigenous mud with sand and silt below Bering Island In the Komandorskiyes. The Kuril-Kamchatka Trench contains fine clay and terrigenous mud combined with siliceous ooze and the western branch of the Emperor Seamounts Chain is covered with siliceous ooze mixed with volcanic material. To the north, between the west branch and the Aleutian Trench, a wedge of pelagic clay with siliceous ooze is present) to the southwest sand, silt and siliceous mud predominate. The northern wall of the Aleutian Trench, immediately below Bering and Mednl Is lands, has an area of clay mixed with sand and silt. Another clay area is shown on the north wall of the Aleutian Trench to the west of the Near Islands. This distribution of sediment reflects present-day sedimentation patterns and processes to the extent that the samples are representative of the areas outlined. The samples are only surflcial, and it is likely that most were recovered from the upper few meters of sea-floor. Horn and others (1970) divided the North Pacific into two separate basins with the Emperor Seamounts Chain Figure 5. Distribution of surface sediment in the trench convergence area (after Frazer and others, 1972). The topo graphy is from Chase and others (19/0). See Plate 1 for geographic reference. The original of this chart is in color. KEY Black. Dark Gray Medium Gray Light Gray White Dots Diagonal Circles Clay and siliceous ooze - Clay - Siliceous ooze and mud - Siliceous ooze - Mud (except for land areas) - Sand and silt - Volcanic material - Rocks and gravel Numbers are locations of individual samples on which the chart is based, 3 « rock and graveli 4 ■ sand and sllti 5 * calcareous oozet 6 ■ sili ceous oozei 7 ■ clay which is mostly (but not always) pelagici 8 “ terri genous mud. 103 104 as the dividing barrier. They further delineated three orders of sedimentary provinces within the basins. Thus the Aleutian and the Kuril-Kamchatka Trenches are con sidered to be third order provinces typified by deposits of turbidltes and associated terrigenous mud and clay. In the area south of the trench convergence the sea-floor to the west and southwest of the Emperors is labeled a first- order province and is characterized by "pelagic muds of finest terrigenous fractions combined with radiolaria, diatoms, ice-rafted detritus and volcanic silt and clay." It is called the Japan-Kuril Province. The area of the seamount chain itself is considered to be a second order province where the type of sediment is "dependent upon the depth of the crests of the submarine highs.” The area to the east of the Emperor Seamounts province is called the Aleutlan-Alaskan province and is considered first-order. According to Horn and others (1970) both the Japan-Kuril and the Aleutian-Alaskan provinces are dominated by mud with intercalated ash horizons, the ash providing a basis for distinguishing the two provinces (brown and white ash for the Aleutian-Alaskan province and only white ash for the Japan-Kuril province). The Aleutian Trench Is the site of turbidite fill with brown volcanic silt and sand deriving from the Aleutian Ridge. Terraces on the north wall of the trench likewise contain trapped, or ponded, turbidltes with poorly defined beds of graded volcanic 106 arenite and lutite. The Aleutian Trench sedimentary environment is considered to represent the Kurll-Kamchatka Trench. No cores are available from the latter. Opdyke and Foster (1970) studied the magnetic stratigraphy of 114 piston cores in the North Pacific and related it to the radiometric time scale for the past 4,5 m.y. of earth history. One of the intriguing conclu sions of their study is that pelagic red clay accumulates at the rate of 3mm/1000 years in the Central Pacific and that rates of sedimentation Increase as one approaches the margins of the Pacific Basin (probably because of in creased volcanic, biogenic, and glacial Influences as well as proximity to the processes of continental erosion). Although the maximum thickness of sediment measured by Ewing and others (1968) in the Pacific Is 400-500 m near the Shatsky Rise, Opdyke and Foster (1970) stated that other areas in the Pacific have thicker sections. They further suggest that the Shatsky Rise section probably represents only the greatest accumulation of pelagic sediments. Another conclusion is that the lowest sedi mentation rate one would expect for the Pacific is 1 mm/ 1000 years. Conolly and Ewing (i970) consider the part played by Ice-rafted detritus in sediment accumulations found in the northwest Pacific. They conclude that the ice-rafted component (1-10 percent of the sand fraction) is slgnlfi- 107 cantly large In the area of the trench convergence and that Pleistocene surface currents, similar to those that flow today, were responsible for the distribution ob served . RESULTS--INTERPRETATIONS AND IMPLICATIONS OF THE GEOLOGICAL AND GEOPHYSICAL DATA The primary products of this investigation are the interpreted seismic reflection profiling data. These data are shown on the accompanying platest detailed interpreta tions are given in Appendix A. Plates depicting the graphic interpretation of each seismic reflection profil ing transect follow each plate of original record. Be cause of this the discussion in this section of the dis sertation is of a summary or general nature. Sediment Thickness and Distribution The three-layer nature of oceanic crust above the mantle finds fairly clear expression in the trench con vergence area, especially for Layers 1 and 2. The concept of layering in the oceanic crust is widely accepted and is basic to any consideration of problems in deep sea strati graphy* structure and tectonics. Many authors have des cribed the layering. Layer 1* whose thickness ranges from a few hundreds to some thousands of meters* consists of soft sediment which is accumulated from debris eroded from the continent and sea-floor sources together with the siliceous and carbonaceous remains of micro-fauna and flora 108 109 and dlagenetlc material. The surficial portions of the pelagic, hemipelagic and terrigenous deposits--muds, oozes, red clays, and turbidites--which make up the bulk of Layer 1 are, for the most part, fairly easy to sample where they can be reached, and are easily studied by seismic reflection profiling techniques. Layer 2, per haps 4 km thick in most places, is considered by some geologists to be higher density material originally com posed of Layer 1 material but now lithlfled and penetrated by dikes and sills, or covered with alternating lava flows. Others consider Layer 2 to be all, or nearly all, basaltic flows, dikes and silts. The top of Layer 2 is generally coincident with the top of the "acoustic base ment" where "acoustic basement" is defined as that material which can no longer yield diagnostic internal or subbottom reflections. J01DES holes, typically, bottom in basalt which either forms the upper portion of Layer 2 or represents sills of basalt in sediments not far above the Layer 1-Layer 2 interface. If the sediment Immediately above is datable, and if the sediment-basalt contact is deposltlanal, a minimum age to the underlying basalt can be assigned. Assuming that this basalt formed at, or near, a spreading center, such ages can be used for deter mining spreading rates, sedimentation rates, etc. The third layer, possibly 7-8 km thick, is known primarily from seismic refraction studies and teleseismic observa- 110 tlons. It Is believed by some to be a great basalt flow originating In the mantle and by others to be a phase differentiate of primary mantle material. It is variably called the "main crustal layer.** the "basaltic** layer or, simply, the "oceanic** layer. Dietz (1961), originally believed that the oceanic layer was gabbro which is a low pressure, low temperature, phase of denser mantle rock, ecloglte. However, more recent studies suggest that the main (third) crustal layer is composed largely of meta morphosed mafic volcanic and plutonlc rocks (Green, 1972i Miyashiro, 1972* Christensen,1970). Where the base of Layer 1 is datable, and the thickness of the layer is known, a gross or average sedi mentation rate can be determined. Given ages and thick ness of intermediate layers, intermediate rates can be assigned and an overall curve established showing the change of sedimentation rates with time. Thus, the thick ness of the sediment column over the acoustic basement and the rate at which it was deposited are critical parameters for assessing both the geographic and environmental site where the deposition took place, and any movement of the underlying plate which would have transported the sediment since it was deposited. The implications of deep sea sediment deposits with respect to the new global tectonics and JOXDES drilling are further discussed by Ewing and Ewing (1970). Ill Oceanic Areas A Pelagic sediments, In varying thicknesses, are recognized seaward of the two trenches on all the acoustic reflection transects of the sea-floor of the two trenches. Their signature Is clear and they are Interpreted as pelaglcs with confidence. They are characterized by a strong lower boundary which Is called the acoustic base ment and is considered to be the top of oceanic crustal Layer 2. Structures within the "acoustic basement" are undiscemible which, of course. Is one of the character istics which defines "acoustic basement." The acoustic basement can be seen to penetrate the sea-floor and form seamounts (refer especially to Lines B-30 and B-31, Pis. 4, 5, 6, and 7) or to rise up, unexposed, close to the Pelagic sediments are considered by Kuenen (1950) to be characterized by the absence of terrestrial mineral grains and to be commonly made of clay minerals and the remains of plankton tests. Hemipelagic sediment com prises materials possessing essentially the same physical characteristics, but having a terrigenous origin. Thus, depending on the environment, hemipelaglcs may contain terrigeneous blue mud, coral mud and sand, calcareous mud, volcanic ash, glacial marine sediments, etc. The distinc tion Is primarily genetic and for purposes of this dis sertation is considered Important only insofar as sources of sedimentation and sedimentation rates are concerned. Although the sediments south of the convergence undoubted ly contain both pelaglcs and hemipelaglcs, they are refer red to as ’pelaglcs' for the sake of convenience and their recognition follows the criteria of Hamilton (1967). 112 sea-floor* Acoustic basement appears also to be exposed along some fault scarps. Reflectors within the pelagic sections are seen in practically all the transects. Two are especially note worthy f one close to the bottom of the section and one close to the top. Pelaglcs between the lower reflector and the acoustic basement have arbitrarily been called the "older" pelaglcs and those betwen the two reflectors "younger" pelaglcs. The section between the reflector which Is close to the top of the section and the sea- floor has been labeled "recent" pelaglcs. but not with confidence. The section between these two prominent re flectors also has reflectors within It permitting, in some places, a further subdivision into "lower" younger pela- gics and "upper" younger pelaglcs. These assignments were made prior to the drilling of JOXDES 192 which geologically corroborated the acoustically defined divi sions (see Lines B-43-20). While the total thickness of the pelagic section is a critical element to the main arguments to be developed in this thesis, the subdivisions 4c 'Recent* pelaglcs is a rather tenuous and not especially useful subdivision because much of it lies in the zone of the 'bubble pulse* effect. However, the average thickness of the layer measured in the seismic section correlates with the surface layer penetrated by JOXDES 192. The core log showed this layer to contain much ash and ice rafted material. 113 within the section are also of interest. They suggest different types of pelagic sedimentation and events or shifts in the source areas rather than dlsconformitles at the site. Thickness of the pelagic sediments was determined for every half-hour interval of track where pelaglcs were exposed and an acoustic basement discerned. The bulk of the measurements were in oceanic areas seaward of the trench, but additional ones were made shoreward or ridge- ward of the trenches where pelaglcs were also Interpreted as being present. The technique of thickness measurement (Appendix B) assumed a linear sound velocity gradient in the sediment and followed the procedures of Hamilton (1971). Curves for determining true bottom depth from echo sounder depth and bottom water velocity from true depth are given in Figures 5 and 6 and the results are summarized in Table 7. Thicknesses of pelagic deposits ranged from 0 to 1600 m seaward of the trenches in most instances• The 152 measurements of Table 8 were plotted an the Chase and others (1970) chart (PI. 1) to determine the distribution of thickness (isopachs) of the pelagic layer. The results are shown In Figure 8. Because of wide variation In thickness and the reduced control re sulting from the large distances separating the control lines, the lsopach map is generalized. A considerable Figure 6. Curve for correcting echo sounder depth to true depth when echo sounder is calibrated for velocity of sound in water of 4800 feet per second. If soundings are made based on velocity of 1500 m/sec (common practice with non-English nations) the depth is converted to 1-way travel time for the compresslonal wave, and thence into fathoms or feet so that corrections for the velocity of sound in water can be applied. This curve is based on a hydrographic cast taken at latitude 52o30' N, longitude 162030' £, on the seaward flank of the Kuril- Kamchatka Trench (Buffington and Hamilton, 1972). 114 K M O IO U N O IR DCPTH (FATHOMS) FMNN KM O IO IA M W M M **M FOt VMOCltT O f MONO M W A IH OF M M 1-p.i | Tabic 7. Data for determination of layer thickness of oceanic pelaglcs (Layer I) and pelagic offscrapings Time (Z) and date (J.D.) Water depth l^ray travel (sec) Water depth (fathoms) 9 4800 fps True water depth (m) Bottom water velocity (m/s) 2 Bottom sediment velocity wyw (m/§) Layer3 thick ness tt£H )sec) Velocity^ at depth "t" (m/sec) Layer thick ness (m) (225) LINE B-30 1115 4.793 3834 7278 1584 Aleutian Border - Aleut. Tr. Floor 0 0 0 1155 4.760 3808 7242 1584 Oceanic Border - Aleut. Tr. F I oot 0 0 0 1207 4.565 3652 6913 1578 Edge of Oceanic Pelaglcs 0 0 0 1215 4.267 3414 6437 1569 1553 0.15 1745 247 1230 4.280 3424 6463 1569 1553 0 . 2 0 1814 336 1300 3.815 3052 5739 1556 1540 0 . 2 0 1799 333 133d 3.810 3048 5724 1555 1539 0.16 1743 262 1400 3,270 2616 4901 1540 1524 0 . 1 0 1647 158 1430 3.120 2496 4672 1536 1521 0.27 1876 457 1500 3.000 2400 4486 1532 1517 0 . 1 0 1640 158 1510 3.053 2442 4572 1534 1519 0.32 1948 552 1530 2.970 2376 4 4 4 4 1531 1516 0.36 2005 630 1600 2.881 2305 4307 1529 1514 0.05 1573 77 1630 2.835 2268 4237 1528 1513 0.15 1700 241 , Corrected for velocity of-sound In water baaed on hydro-cast at 0 52'3l'N - 162a30'E , Botton sediment velocity * bottoe water velocity x 0,99 (Hamilton, 1971) ^ From seismic reflection profiling records Based on sound velocity gradient In sediment of 0.777 m/sec/m measured at JOIDES 192 Tims (Z) Hater and date depth (J.D.) 1-way travel (eec) Hater depth (fathoM) 9 4800 fps True* vater depth (■) Bottoe water velocity (■/*) LIME B-30 1700 2.230 1784 3319 1520 1730 2.955 2364 2425 1497 1800 3.385 2708 5080 1544 1830 3.345 2676 5014 1542 1900 3.270 2616 4901 1540 1930 2.960 2368 4426 1531 200CT 2.880 2304 4307 1529 2030 2,865 2292 4281 1529 2100 2.805 2244 4195 1527 2131 2.527 2022 3771 1520 2200 2.433 1946 3626 1517 (225) LIKE 8-31 2230 2.538 2030 3789 1520 2250 2.633 2106 3932 1524 2300 2.590 2072 3877 1522 2330 2.675 2140 4005 1524 2400 3.137 2510 4713 1537 (228) 0030 3.295 2636 4947 1541 0050 3.280 2624 4932 1541 0100 3.265 2612 4903 1540 0130 2.320 1856 3456 1515 0200 3.000 2400 4499 1532 0230 3.4i0 2728 S124 1545 Bottoe2 Layer1 sediment thick- velocity ness f t y t l (e/S) (sec) Velocity" Layer at depth thick "t" ness (a/sec) (e) (con't) Seamount - Exposed basement 0 0 0 Seaaount - Exposed basement 0 0 0 1529 0.47 2203 867 1527 0.40 2084 716 1525 0.47 2197 865 1516 0.37 2 0 2 1 650 1514 0.50 2233 925 1514 0.50 2233 925 1512 0.45 2145 815 1505 0.23 1799 379 1502 0.25 1824 414 1505 0.18 1731 291 1509 0.19 1749 309 Seaaount - Exposed basement 0 0 0 1509 0 . 1 0 1631 157 1522 0.16 1723 259 1526 0.38 2050 675 1526 0.50 2250 932 Seaaount - Exposed baseaent 0 0 0 Seaaount - Exposed basement 0 0 0 Seamount - Exposed basement 0 0 0 1529 0.28 1901 478 Time ( 1 ) and data (J*D.) Hater daptb 1-way travel (eec) Hater depth (fathone) 0 4800 fps True1 water depth (■) Bottom water velocity (n/s) Bottom sediment velocity *»y *t (m/8) Layer thick ness * # £ » ! (sec) Velocity at depth If^ lt (m/sec) Layer thick ness (■) 0300 3.650 2920 5486 1551 1535 0.35 2015 617 0330 3.650 2920 5486 1551 Exposed acoustic basement 0 0 0 0400 4.068 3254 6136 1563 Exposed acoustic basement 0 0 0 0410 4.167 3334 6291 1566 1550 0.15 1742 247 0420 4.420 3536 6684 1573 1557 0.25 1891 430 0430 4.620 3696 7004 1580 1564 0.25 1899 432 0430 4.620 3696 7004 1580 Oceanic border - Aleutian Trench floor 0455 4.620 3696 7004 1580 Aleutian border - ■ Aleutian Trench floor (226) LINE B-32 0715 Trench axis. Bo turbldltes or flat floor evident. 1Pelagic section measurable 0715 4.550 3640 6895 1577 1561 0 . 2 0 1823 338 0730 4.400 3520 6657 1573 1557 0 . 2 0 1819 337 0800 4.025 3220 6062 1562 1546 0.25 1877 427 (226) LIME B-33 0632 3.950 3160 5953 1560 1544 0 . 2 0 1804 334 0900 4.165 3332 6276 1566 1550 0.17 1769 282 0930 4.440 3552 6715 1574 1558 0.25 1892 430 0945 4.557 3646 6904 1577 1561 0.23 1866 393 0945 Oceanic border - Aleutian Trench. Flat trubidlte floor meets oceanic pelaglcs. 1 0 0 0 Aleutian border • - Aleutian Trench. *• (a) i d date J.D.) (224) 2128 2130 2200 2230 2245 2300 2330 2400 (227) 0030 0100 0130 0200 0230 0300 0330 0400 0430 (227) 0500 0530 0600 0630 0700 Water depth 1-way travel (eec) Water depth (fathaae) * 4800 fpa True1 water depth (a) Bottom water velocity (■/*) Bottom sediment velocity i t y ' • (m/s) Layer3 thick ness n ^n (sec) Velocityk at depth (■/sec) LINE B-36 Northern border of pelagic body lying rldgeward of Aleutian Trench 4.075 3260 6145 1563 1547 0.35 2030 4.025 3220 6062 1562 1546 0.42 2143 4.450 3560 6734 Aleut, bord . - Turbs. and flat bot. Aleut, Tr 4.460 3568 6748 Ocean, bord.. - Turbs. and flat bot. Aleut. Tr 4.030 3224 6075 1562 1546 0.35 2029 3.695 2956 5560 1552 1536 0.45 2179 3.55; 2844 5351 1548 1533 0.35 2 0 1 2 3.185 2548 4782 1538 1523 0.25 1850 3.350 2680 5033 1543 1528 0,45 2168 3.255 2604 4892 1540 1525 0.39 2065 3.225 2580 4846 1539 1524 0.42 2 1 1 2 3.135 2508 4715 1537 1522 0.49 2227 3.060 2448 4590 1534 1519 0.55 2329 3.065 2452 4596 1534 1519 0.59 2402 2.965 2372 4444 1532 1517 0.16 1735 2.780 2224 4162 1536 LIKE 8-37 1521 0.25 1847 3.035 2428 4590 1535 1520 0.25 1846 3.185 2548 4782 1538 1523 0.48 2 2 1 1 3.190 2552 4791 1538 1523 0.47 2194 3.245 2596 4874 1540 1525 0.48 2214 3.195 2556 4791 1538 1523 0.50 2246 Tine ( 2 ) Hater and data dapth (J.D.) 1-way travel (aac) Hater Tru* 1 depth water (fathoaa) depth 8 (■) 4800 fps Botton Bot to* 2 water sediaent velocity velocity (■/*) ”V " (■/S ) Layer1 Velocity1 * thick- at depth aess "t" "t" (n/sec) (eec) (227) 0730 3.180 2544 0800 3.045 2436 0830 3.290 2632 0900 3.560 2848 0930 3.620 2896 1 0 0 0 4.105 3284 1030 4.615 3692 1030 4.615 3692 1 1 1 0 4.615 3692 (227) (228) 1216 Morthern border < 1216 4.100 3280 1 2 2 0 4.133 3306 1230 4.090 3272 1240 3.880 3104 1300 4.433 3546 1325 Aleutian border 1345 Oceanic border - (228) LIME B-37 (con * t) 4773 1538 1523 0.37 2030 4572 1534 1519 0.43 2 1 2 2 4947 1541 1526 0.30 1927 5358 1549 1534 0.45 2176 5450 1550 1535 0 . 1 0 1659 6190 1564 1548 0.17 1785 7002 1579 1563 0.35 2051 7002 Oeeah. bord. - Turbs. and flat bot. Aleut. Tr. 7002 Aleut, bord. - Turbs. and flat bot. Aleut. Tr. LIME B-38 Morthern border of pelagic body lying rldgevard of Aleutian Trench. ' .......... 4181 1564 6236 1565 1549 0.35 2033 6163 1564 1548 0.20 1808 M65 1558 1542 0.50 2274 6712 1574 1558 0.25 1892 lat turbldlte Aleutian Trench Floor at turbldlte Aleutian Trench Floor >.50 — Layer thick ness (■) 653 776 516 626 159 284 629 000 623 335 942 430 >900 120 ■e ( 8 ) d date J.D.) (228) 2000 2035 2100 2130 2200 2230 2300 2330 2400 (229) 0030 0100 0130 0200 0230 0300 0330 0400 0430 0500 0530 0400 0630 0700 0730 0800 Veter Veter True Bottom Bottom depth depth water water sediment 1-way (fathoms) depth velocity velocity travel 8 (■) (m/a) "V " (s a c ) 4800 fpa (m /S ) Layer thick ness (sec) Velocity" at depth (a/sec) Layer thick ness (■) LINES B-42. 43 4.470 3576 6766 Approx. Aleutian border - Aleutian Trench floor. 4.446 3557 6730 Oceanic border - Aleutian Trench floor. 3.948 3158 5944 1560 1544 0.30 1949 522 3.517 2814 5294 1547 1531 0.45 2172 825 3.395 2716 5102 1544 1529 0,45 2169 824 3.260 2608 4901 1540 1525 0.45 2163 822 3.205 2564 4819 1539 1524 0.50 2247 931 3.070 2456 4609 1535 1520 0.69 2558 1336 2.960 2368 4438 1531 1516 0.65 2512 1282 2.890 2312 4334 1530 1515 0.69 2589 1383 2.825 2260 4234 1527 1512 0.65 2505 1278 2.700 2160 4042 1524 1509 0.65 2501 1276 2.600 2080 3890 1522 1507 0.69 2576 1376 2.550 2040 3809 1520 1505 0.55 2307 1032 2.455 1964 3667 1518 1503 0.55 2304 1031 2.415 1932 3603 1517 1502 0.64 2470 1245 2.305 1844 3438 1514 1499 0.45 2126 807 2 . 2 0 0 1760 3274 1511 1496 0.69 2557 1365 2.250 1800 3347 1512 1497 0.74 2660 1497 2.205 1764 3279 1511 1496 0.80 2785 1659 2 . 0 1 0 1608 2981 1506 1491 0.50 2198 911 2.030 1624 3014 1507 1492 0.48 2166 8 6 8 2 . 1 2 0 1696 3146 1509 1494 0.40 2039 701 2.225 1780 3310 1512 1497 0 . 2 2 1776 359 2.510 2008 3749 1519 1504 0.07 1588 108 121 I ) 125 174 330 330 296 422 331 490 424 461 591 557 423 598 619 464 563 486 433 181 216 Water Water depth depth 1 -way (fathoms) travel 0 4800 fp« True1 water depth (a) Bottoe water velocity (■/■) Bottom2 sediment velocity • * y H (■/S) Layer1 thick ness (eec) Velocity4 at depth (■/sec) LINES B-42, 43 (can't.) 2.705 2164 4051 1525 1510 0.08 1607 3.040 2432 4557 1534 1519 0 . 1 1 1655 3.210 2568 4819 1539 1524 0 . 2 0 1780 3.340 2672 5024 1543 1527 0 . 2 0 1784 3.420 2736 5139 1545 1530 0.18 1760 3.460 2768 5205 1546 1531 0.25 1859 3.475 2780 5225 1546 1531 0 . 2 0 1788 3.565 2852 5358 1549 1534 0.29 1921 3.600 2880 5413 1550 1535 0.25 1864 3.625 2900 5457 1551 1535 0.27 1893 3.680 2944 5545 1552 1536 0.30 1939 3.550 2840 5340 1548 1532 0.32 1964 LINE B-44 3.551 2840 5340 1548 1532 0.25 1860 3.700 2960 5569 1553 1537 0.34 2 0 0 2 3.780 3024 5688 1555 1539 0.35 2 0 2 0 3.960 3168 5962 15^ 1544 0.27 1904 4.160 3328 6273 15f 6 1550 0.32 1988 4.340 3472 6560 1571 1555 0.28 1933 4.780 3824 7264 1584 1568 0.25 1904 5.000 4000 7608 1591 1575 0 . 1 1 1716 5.020 4016 7644 1592 1576 0.13 1743 Trench axis 4.533 3626 6867 1577 1561 0.70 2689 average estimated thickness for off-scrapings which continue until = 19458 Time (B) Water Water True Bottom and data depth depth water water (J.D.) 1-way (fathom) depth velocity travel 8 (m) (m/a) (sec) 4800 fpa Bottom sediment velocity I ty It (m /8) Layer thick ness flg tl sec) Velocity' at depth Tig It (m/sec) Layer thick ness (m) (231) 0130 Pelagic offscraplngs Indicated LIKE B-45 as ending here on interpretative overlay. 0330 4.160 3328 6276 1566 1550 1 . 0 0 3371 2343 0400 4.345 3476 6574 1571 1555 0.75 2785 1583 0425 Trench axis. Floor la flat, very narrow but without turbldites. 0430 4.765 3812 7242 1583 1567 0 . 2 0 1830 339 0500 4.120 3296 6209 1564 1548 0.35 2032 623 0530 3.665 2932 5510 1551 1535 0.26 1878 442 0600 3.240 2592 4868 1540 1525 0.28 1896 477 0630 2.910 2328 4362 1530 1515 0.15 1702 241 0700 2.455 1964 3667 1518 1503 0.25 1825 415 0724 2.373 1898 3537 1516 1501 0.24 1809 396 (231) 1130 2.133 1706 3182 LIKE B-46 1510 1495 0.47 2153 848 1 2 0 0 2.247 1798 3347 1512 1497 0.47 2157 849 1230 2.345 1876 3493 1515 1500 0.42 2079 745 1301 2.420 1936 3612 1517 1502 0.40 2049 705 1330 2.655 2124 3968 1523 1508 0.29 1889 491 1400 3.050 2440 4572 1534 1519 0 . 1 0 1642 158 1430 3.400 2720 5111 1544 1529 0 . 1 0 1652 159 1500 3.745 2996 5633 1554 1538 0.40 2096 722 1530 4.160 3328 6273 1566 1550 0.40 2115 727 1530 1800 * Trench axis Shoreward termination of pelagic off scrapings (?) • thickness over the trench axis .« (2) id date J.D.) tfater depth 1-way travel (eec) Water depth (fathoms) 8 4800 fps True1 water depth (■) Bottom water velocity (■/a) Bottom2 sediment velocity I t y I I (m/s) Layer thick ness I I ^ H (sec) 1 Velocity* at depth (■/sec) Layer thick ness (■) (232) LINE B-47 0930 Sbonvard termination of pelagic offscraplngs as Indicated on Interpretative overlay. 1 1 0 0 3.885 3108 5870 1558 1542 0.97 3276 2232 1130 4.100 3280 6181 1564 1548 0.67 2605 1360 1140 Trench axis 1 2 0 0 3.805 3044 5733 1556 1540 0.48 2236 896 1230 3.890 3112 5858 1558 1542 - - - _ * 1300 3.660 2928 5505 1551 1535 0.75 2749 1563 1330 3.375 2700 5075 1544 1529 0.71 2655 1449 1400 3.145 2516 4718 1537 1522 0.60 2425 1163 1430 3.0o0 2448 4590 1535 1520 0.70 2619 1414 1500 3.005 2404 4507 1533 1518 0.36 2008 631 1531 2.830 2264 4243 1528 1513 0.30 1910 511 Uoo 3.200 2560 4810 1590 1574 0 . 2 0 1838 341 (232) LINE 8-48 1608 3.267 2614 4910 1541 1526 0 . 1 0 1649 159 1620 3.300 2640 4937 1541 1526 0.35 2003 614 1630 3.400 2720 5111 1544 1529 0 . 2 1 1800 349 1700 3.915 3132 5874 1558 1542 0.55 2364 1058 1730 4.160 3328 6273 1566 1550 0.85 3000 1866 1745 Approximate ayts of Aleutian Trench - no flat bottom - no turbldltes. 1745 4.207 3366 6346 1567 1551 1 . 0 0 3373 2345 1800 4.060 3248 6117 1563 1547 0.40 2 1 1 0 726 1830 3.810 3048 5733 1556 1540 0.44 2168 808 1900 3.565 2852 5367 1549 1534 0.72 2684 1480 1920 3.807 3046 5733 1556 1540 0.15 1730 245 124 Figure 7. Curve for determining water velocity from true (corrected) depth. This is based on a hydro- graphic cast at latitude 52°30> N, longitude 162°30' E on the seaward flank of the Kuril-Kamchatka Trench Buffington and Hamilton, 1972). It has been determined that this curve and the preceding depth correction curve (Fig. 5) are representative for the entire oceanic portion of the northwest Pacific Ocean (E. L. Hamilton, personal communication). 125 126 •OTTOM W A T II VHOCirr IM IT tR t/a K O M ftt IMP U00 . >100 - « 1000- Figure 8. Ieopach chart of pelagic sediments in the area south of the trench convergence. The chart is con structed from the data presented in Table 8* 127 I ' l % ca nratio sascm cnt, s e a m o u n ts , o> TtCNCH UM OHIAM OHIT IT TUHHMTCS • AXIS o r KMH-KAMCHATKA AMO N.W M IT OF ALEUTIAN THMCHfS AmOXUHATI LIMITS- PUT HOOF OF ALEUTIAN TMMCH THICKNESS OF FELAGIC SEDIMENTS IN AREA OF A LEUTIAN-K AMCH A TK A TRENCH CONVERGENCE COMTOIM INTEEVAL-IOOOM ..I. IM * 128 129 subjective interpretation is involved in drawing the isopach lines( however, a definite pattern emerges, as follows t 1. The bands, or patterns, of thickness are separated by the Emperors. 2. The bands northeast of the Emperors parallel the trend of the Aleutian Trench, 3. The thickest body of sediment is between the Emperors and the Aleutian Trench, and extends in a long tongue from the convergence proper to the southeast, rough ly parallel to the Aleutian Trench and Ridge. 4. Generally, the sediments are thickest landward of the trenches near the convergence (at least 2345 m), and thin to the southeast, where they are less than 500 m east of longitude 172° E. 5. Sediments thicken as one proceeds from the Aleutian Trench to the Emperors and then thin to the south west going from the Emperors to the Kuril-Kamchatka Trench. 6. With local exceptions, the sediment to the southwest of the Emperors (i.e., between the Emperors and the Kuril-Kamchatka Trench) Is substantially thinner than that to the northeast (i.e., between the Emperors and the Aleutian Trench). 7. The interpretation that the sediment is thick est at the convergence and thins with distance indicates a 130 primary source at the convergence. Thus the nearby Kamchatka Peninsula, the Komandorskiye Islands, and sedi ment transported from the Kamchatka Basin In the Bering Sea south through the strait between Bering Island and Cape Kamchatskly would be primary sources. 8. The interpretation that the sediments are much thicker to the northeast of the Emperors than to the southwest suggests a definite topographic control over sedimentation with the Emperors acting as a sediment bar rier as suggested for modem day sedimentation by Horn and others (1970). Ewing and Ewing (1970, Fig. 5) show an isopach map for Cenozoic sediments of the northwest Pacific which indicates southwest-northeast trending lsopachs and a thickening toward the convergence from the southwest. This part of the map is generally correct. Thicknesses are given, however, in units of reflection time (2-way travel) with 0.1 sec. equal to about 1000 m. Assumed interval velocity appears to be about 2000 m.p.s. which is imprecise and much too high for the area. Inspection of Table 8 shows more nearly correct thicknesses. Ewing and Ewing's (1970) chart also fails to indicate any in fluence by the Emperor Seamounts. Each of the basic seismic reflection profiles and interpretative overlaps (Pis. 4 through 25, exclusive of those few lines which show no pelaglcs) constitute a cross- Table 8. HlniwM thickness of turbldltes In the Western Aleutisn Trench Line Let. Long. Water Water Water Min.2 Min.3 Mo. (North) 0 (East) depth 1-way depth (■) depth (fms) True water depth* thick. turb. thick. turb. travel at at (fns) (n) sect. sect. (sec) 1500 n/s 4800 ft/s 1-way travel (sec) (■) **h" B-30 51*55.6* 172*01.0' 4.777 7165 3822 3970 7260 0.73 2075 8-31 52*36.2* 170*06.8* 4.633 6950 3706 3850 7041 0.34 711 1-32 52*38.1* 170*03.7* 4.550 6825 3640 3770 6895 No turbiditcs 8-33 52*47,0' 169*49.5* 4.557 6835 3646 3775 6904 0.14 249 8-36 53*01.3* 168*29.2* 4.467 6700 3574 3700 6766 0.26 509 8-37 53*33.4* 167*57.5* 4.610 6915 3688 3820 6986 0.65 1737 8-38 53*53.4* 166*54.3* 4.470 6705 3576 3702 6770 0.59 1505 8-41 53*50.8* 166*55.2* 4.460 6690 3568 3690 6748 0.67 1818 8-42 53*47.7* 166*56.5' 4.467 6700 3574 3835 7031 0.50 1188 2 Corrected for velocity of sound in water. . fros scisnic reflection profiling records^ 2 Celculsted utilizing regression equation V ■ 1*584 + 1.2830(t) + 0.6032(t ) derived fron sonobuoy solutions for_the Western Aleutian Trench (E. L. Hanilton, personal coMumication) and thickness equation h * Vt. See discussion in Appendix C. 132 section. The section for Lines fi-42 and B-43 (Pis. 14 and 15) Is considered representative because It crosses the entire sea-floor south of the trench Juncture with JOIDES 192 at Its center as a control point. JOIDES 192 Joint Oceanographic Institution Deep Earth Sampling (JOIDES) site 192 data Is considered to be a basic result of this study insofar as the drilling location was select ed on the writer's recommendation after early study of seismic profile B-43 across the Meijl Guyot. The funda mental information from the hole is graphically summarized on p. B-43-20 where it is compared with the predicted section. Scholl and Creager (1973) and Creager, Scholl and others (1973) described and discussed the core mater ial in detail and present sedimentation rates. Trenches The results of sediment determination in the two trenches needs only brief discussion. The four crossings of the Kamchatka Trench show no turbldlte deposition what soever. Any suggestion of a flat floor and layered sedi ments is almost completely lacking. Although it is known that turbldltes and a flat floor exist in the trench ap proximately 200 km (108 n.m.) to the southwest of the point where Line B-44 crosses the axis (Buffington and 133 Hamilton, 1972), the results to the north, reported here, suggests that turbidite sediment Is eitheri 1. Trapped and ponded before reaching the trench, 2. Not generated in the area of the trench (i.e., on either the seaward or landward walls of the trench), or 3. Subducted or scraped off as fast as it forms. Lines B-44, B-45, B-46 and B-47 (Pis. 16 through 23) are all interpreted to show the Kamchatka Trench to be under lain with "younger'* pelagics. In contrast, all crossings of the Aleutian Trench except two (Lines B-32 and B-48) show we11-developed turbldites. The total thickness of the turbidite section in the trench could not be measured because it was not possible to identify the underlying basement with certain ty* However, a minimum thickness was calculated based on one-way travel time from the trench floor to the lowest reflecting horizon identifiable as a turbidite layer. The results are summarized in Table 9. In these calculations a regression equation derived from sonobuoy measurements At made in the western Aleutian Trench (Lines B-41 and B-21) was used (see Appendix B for discussion of the regression equation method). * Line B-21 is near Adak and a short distance to the east of the study area for this dissertation. 134 Table 9. Sedimentation rates Meiji Guyot Joides Drill Site 192* Major Sediment Type for Drilled Interval Thickness Drilled (m) Age Sedimentation Rate mm/thousand years Doatomaceous silty clay and volcanic ash 140 U. Plio. & Holo (3-0 m.y.) 47 Diatomaceous ooze 410 U. Mio. & L. Plio. (8-3 m.v.) 82 Diatomaceous- rich clav 155 M. & U. Mio. (12-8 mtyt) 39 Claystone with minor chalk 235 01ig., L. & M. Mio. (38-12 m.v.) 9 Chalk and clay- stone _ 84 U. & M. Eocene (49-38 m.v.) 7-8 Chalk, some claystone 20 M. & L. Maestrie. 4 (67-72 m.y.) * Taken from Scholl and Creager (1973). 135 Sedimentation Rates Sedimentation rates can be established wherever accurate thicknesses of sediment and absolute ages are known. Where these data are less precise, close estimates can still be made. JOIDES 192 on Meljl Guyot drilled through 1044 m of sediment prior to encountering basalt. The maximum age determined was lower Maestrichian in the Late Cretaceous. According to Berggren (1972) the Cretaceous ended and the Paleogene began 65 m.y. before the present. Therefore, a conservative age for the basal sediment is 70 m.y. B.P. If sedimentation had been steady and continuous from that time until the present, the sedimentation rate would have been about 15 mm/1000 years. In fact, the section at the JOIDES 192 site was thin, relative to adjacent areas, probably because it was on a topographic high and current action transported much of the material elsewhere. Approximately 7 km to the northeast of the JOIDES site an almost identical pelagic section attains a thickness of 1650 m for an average sedimentation rate of 25.4 mm/1000 years. Sedimentation rates for discrete drilled intervals at the JOIDES 192 site an Meljl Guyot are given in Table 9. For the span of time between the present and the lower part of the middle Miocene these rates are 2 to 3 times greater than the average rate for the entire 136 section and exceed, or approximate, the rates for turbid ite sedimentation cited by Hamilton (1967) for the Tufts abyssal plain in the Gulf of Alaska. Sedimentation rates for deep sea pelagic red clay in the central Pacific average about 3 mm/1000 years with the lowest being about 1 mm/1000 years (Opdyke and Foster, 1970). For pelagic clay overlying the turbidites of the southern part of the Aleutian Abyssal, Hamilton (1967) cited rates of 1 mm/1000 years, 2 mm/1000 years, and 5 mm/1000 with the 2 ram rate preferred. Changes in sedimentation rate resulting from cal culations made on an "uncompactedN section (before con solidation takes place) are not considered to be signifi cant according to Hamilton (1967). His calculations, based on measurements taken at the Guadalupe experimental Mohole site indicate that consolidation in deep-sea sedi ment reduces the thicknesses of the upper layers by amounts on the order of 5 percent. However, the claystone at JOIDES 192 has cora- pressionally flattened foraminiferai further, consolidation teats indicate that original thicknesses have been reduced by one-half. The discrepancy between Hamilton's figures and those of JOIDES 192 result from the exceedingly high rate of sedimentation for much of the material cored at JOIDES 192 where the rapidly deposited sediment had a very high interstitial water content* The present consolidated 137 density of this claystone is 2.0-2.1 (Scholl and Creager. 1973). Also of considerable significance is the discovery that, although diatoms constitute a large percent of the upper 410 m of the JOIDES 192 section, they are associated with terrigenous and volcanic detritus. The uncompacted rate of infall of this non-biogenic material has been re constructed by "subtracting" the diatom fraction. It has not changed much, averaging around 40 mm/thousand years since the early middle Miocene, or possibly before. Thus the increase in total sedimentation rate noted (Table 9) for the late Miocene can be related to an influx of diatoms, the rate of terrigenous sedimentation remaining essentially unchanged (Scholl and Creager. 1973). What caused this onset of diatom productivity in the late middle Miocene is unknown. Scholl and Creager (1973) noted that the phenomenon "is consistent with the existing location of Site 192 beneath the confluence region of the south-flowing and cold Oyashio current and the warmer waters of the northwest Pacific." The implication is that site 192 was at or near its present location at that time. It is clear that the sedimentation rates at the JOIDES 192 site for the period since the middle Miocene are more than an order of magnitude larger than rates for deep-sea sedimentation at great distances from terrestrial 138 sediment sources. Peninsular and Insular Margins The structure and the sediments of the peninsular and Insular margins, especially in the areas of the inner trench walls and the terraces, are so closely Interrelated that it is virtually impossible to separate them for pur poses of Individual discussion. Indeed, it would be con fusing to do so. Thus, there is a great deal of structure discussed in the sections on sediments which follow. Cor respondingly, the pages on structure necessarily require supporting information and discussion of sediments. Aleutian and Kamchatka Shelves Shelf sediments around the Near Islands were des cribed by Scruton (1953). They contain a variety of volcanic and glacial marine sediment. Zhegalov (1964) commented on the lack of evidence of Quaternary glaciation on the Komandorsklyes and speculated that any existing glacial deposits may have been eroded as a result of Quaternary uplift. Whether traces exist on the shelves of the Komandorsklyes is unknown. Only small sections of the insular shelves were crossed in the 1970 expedition and sampling there was not one of the expedition object ives. As revealed in the seismlc-reflection profiles, the shelves are bedrock with a relatively thin veneer of 139 sediment. Bottom sampling of the continental shelf in Russian waters is forbidden by international agreement. Line B-44 (Pis. 16 and 17) crossed the outer portion of the Kam chatka shelf off Cape Kronotski and a section of sediment approximately 0.1-0.2 seconds thick was measured. The section shows structural characteristics of a delta, namely, foreset bedding. It is possible that this is a clue to the regimen supplying sediment to the offshore basins of the Kamchatka Terrace. Aleutian and Kamchatka Terraces The Aleutian Terrace is not the well-developed feature in the western Aleutians that it is along the central and eastern portion of the ridge. Some of the ridge crossings (Lines B-35, B-36 and B-38| Pis. 6, 7, 8, 9, 12 and 13) show well-developed structural basins which are sediment traps for debris originating on the ridge. These are considered to be the "terrace,** such as It is. The basins are doubtless local, making the terrace dis continuous, a condition which is corroborated by examining the relatively crude bathymetric data available. The function of the basins as sediment traps Inhibits the transport of turbidites to the trench, but may not prevent it. Trench turbidite deposits are apparently nourished by material transported down inter-basin canyons and by 140 flows coming down the axis of the trench from shoaler areas to the northwest. Axial transport from Alaska is another source) in addition* the Kamchatka Basin in the Bering Sea could supply the western trench by way of Kam chatka Pass (between Bering Island and Cape Kamchatskiy on the Kamchatka peninsula). Occasionally a small turbid ite channel or basin is present either within one of the larger basins (Lines B-35 and B-38| Pis. 6, 7, 12 and 13) or as a solitary feature of the bedrock of the ridge (Lines B-30 and B-37) Pis. 4, 5, 10 and 11). In some in stances these local turbidite deposits are tilted toward the trench, in others they are flat and at one site they are back-rotated toward the ridge. All of this signifies fairly recent local tectonlsm on the ridge. The Kamchatka Terrace is not a "terrace** in the strict definition of the termj however, it is, to a large extent, a topographic and structural corollary to the Aleutian Terrace. As shown by Lines B-44 and B-45 (Pis. 16-19), the striking feature of the terrace is the im mensely thick (>> 1.6 seconds) est. 4.5-5.0 km) section of sediment which it comprises. There is little question that this feature is contributory to the absence of sedi ment (turbldltes) in the Kamchatka Trench) however, a puzzle is posed by the fact that the bathymetry reveals drainage paths through the basin to the trench, signify ing that the basin is not completely closed. It seems 141 likely that turbidites should underlie the trench deep (> 4000 fathomsi PI. 1) that lies between Lines B-44 and B-45, but obvious turbidites are generally absent from the floor of the trench. It is not certain whether the "ter race" structural basins are the result of the superimposed sediment load or whether they pre-date the sediment. That the youngest depositional unit, which is about 2500 m (1-2 seconds) thick, thins against the outer high is good evidence that basin formation continued during sedimenta tion. Sediment thickness here is an excellent indication that the Kamchatka Peninsula was actively degrading dur ing the post-Middle Miocene time represented. Large slump bodies, Interpreted to overlie the basin sediments (Line B-44. Pis. 16 and 17) Indicate an unstable tectonic environment similar to the Aleutian Ter race. This is not surprising in the face of the seismic evidence which establishes the Kamchatka continental slope as one of the most tectonlcally active areas in the world. Inner Trench Walls All of the five transects of the north wall of the Aleutian Trench reveal it to be bare of any significant sediment cover. Slumps are interpreted over most of the steep northern wall on Line B-30 (Pis. 4 and 5) but they constitute a relatively thin cover over acoustic basement. With the exception of the basin fill previously discussed. 142 Line B-35 (Pis. 6 and 7) show bare* exposed bedrock of the Early Marine Series (pre-middle or late Miocene). This transect does not have any suggestions of slumps. Line B-36 (Pis. 8 and 9) Is almost identical to Line B-35 in that It has no sediment cover. A body of pelagic deposits about 700 m thick, however, occurs at the base of the wall on this line which separates it from the floor of the trench proper. There is no topographic continuity with the slope— in fact, the body of pelagics is separated from the south ridge wall by an extensive back slope. A possible interpretation is that the body is a giant slump, however, its sheer dimension (>16 km) in the direction of the transect suggests that it may be a narrow segment of oceanic crust, isolating the trench from the base of the Aleutian Ridge. Extensional rifting is or pull-apart phenomena, therefore, implied. This will be discussed on later pages. The insular slope along Line B-37 (Pis. 10 and 11) also is bare of sediment cover and lacks slumps. Except for sparse sediment fill in two small basins it comprises bare bedrock (EMS) to the trench floor. Of interest is the steep angle (> 12%°) of intersection with the floor. Subbottom reflectors, interpretable as the surface of oceanic basement, can be seen on the Aleutian side of the trench axis. If this interpretation is correct, some of the material above may be oceanic, pelagic deposits, much 143 as in Line B-36. There Is no topographic expression of the body as in Lines B-36 and B-38 which makes the inter pretation a second choice to the possibility that the ridge wall descends to meet the trench floor in a "normal" fashion. Line B-38 (Pis. 12 and 13) is significantly dif ferent from all the other wall crossings in that an identifiable sediment section covers almost the entire slope. Immediately south of Mednt Island the slope is slumped on the inner margin of the "terrace" basin which, itself, contains at least 0.8 sec. of Late Marine Series type basin fill. An additional thin layer of Late Marine Series material (corroborated by a dredge haul) covers the lower, steep ( » 16°) portion of the slope. At the foot of the slope, and separating it from the trench floor, is another body of pelagic material similar to that described on Line B-36, an Isolated slice of oceanic crust (pelaglcs of Layer 1). In addition, two small ridges. Interpreted to be pelagic slices, can be seen a slight distance seaward of the larger body* These are separated from each other by small turbidite channels which are measurably higher than the main trench floor. Local tectonic vertical movement, comparable to that found along a rift zone, is the preferred interpretation* In addition, the main channel of the trench has tilted sediment below the top 0.1 sec. and a steep and most 144 peculiar concact with the oceanic pelaglcs of the south wall. This suggests a northward tilting of the sub- trench basement. The transect across the inner wall of the Aleutian Trench south of Bering Island (Pis. 24-25) was inter rupted midway by an equipment shut-down, thus missing about one-half hour (- 8 km). The remaining portion shows essentially bare bedrock as does Bering Island shelf. A thick body of pelagic sediments is interpreted as lying on a bedrock bench on the north side of the trench axis between it and the steeply (>13^°) rising wall of the ridge. The body of sediment is continuous across the trench to the oceanic side. The lowest topographic point is the bottom of a small V-shaped channel which is be lieved to be the trench axis. The channel possibly may be an erosion notch carved by turbidity currents moving rapidly down slope to the east. There are no turbidites within the channel, but approximately 0.2 sec. directly below the axis there are several flattlsh reflectors. These would be suggestive of buried turbidite beds ex cept that their ends are upturned rather than butting against a channel wall. If they are turbidites, they could be the result of a local tectonic event temporarily lowering base level so ponding could occur. A secondary lowering of the central portions could produce the up- tilted margins. Successive vertical movements are lm- 145 plied. As here interpreted all four of the transects of the Kuril-Kamchatka Trench (Lines B-44, 45, 46, 47) ex hibit an inner wall whose lower portions are covered with a thick layer of deformed pelagic sediments. These are considered to be offscrapings from a subducting Pacific Plate. Pelagic layering is also evident on the seaward segments of all of the crossings. On three of the cross ings the reflector marking the top of the acoustic base ment and the bottom of the pelaglcs dips westward beneath the trench and disappears from the record anywhere from 10-15 km shoreward of the trench axis. The shoreward ex tent of the sediments Interpreted as off-scrapings is marked by an abrupt change in the bottom topography be lieved to reflect a sharp contrast in the deposltional units underlying the inner slope. This contrast is es pecially striking on Lines B-44 and B-45 (Pis. 16-19). An alternative interpretation can be made for the sediment of the inner walls of the Kuril-Kamchatka Trench, specifically that this material represents slump deposits at the base of the inner trench slope. Zn this case, the reflectors which extend under the inner wall would be from burled surfaces rather than the result of crustal under- thrusting. Structure 146 Penetration of seismic reflection profiling systems, even at low frequencies, is relatively small when consider ing features of geotectonic dimension. However, some clues are decipherable and these are briefly enumerated. Again, it is virtually impossible to separate the dis cussion of structure from that of the sediment bodies which reflect the structure} thus, some restatement and redescription is inevitable. Deep Sea Areas In addition to the strong layering pattern dis cussed in the previous sections, all transects of the sea- floor south of the area of trench convergence show, to a variable extent, well-developed gravity or normal fault ing. Line B-30 (Pis. 4 and 5) shows a relatively recent graben that appears to have formed after the pelagic layering was almost totally deposited. Both Lines B-30 and B-31 (Pis. 4-7) show seamounts with at least one side exhibiting fault contact with the pelagic section. A few small faults within the surface portion of the pelagic section are evident but these are the exception rather than the rule, as one would not expect to see such features in soft pelaglcs. While shallow (0-100 km) epicenters of modem seismicity are abundant along both 147 Che Kamchatka and Aleutian Trench areas, they are virtual ly absent from the deep sea area immediately south of the convergence (Barazangi and Dorman, 1969). The possible significance of this faulting in the overall geotectonic picture is quickly apparent! it fits nicely into the pat tern of an externally ruptured oceanic plate flexing downward toward the Kuril-Kamchatka Trench. Trench Floors The floor of the Aleutian Trench on Line B-30 (Pis. 4 and 5) has a measurable 0°15* slope to the northeast. Whereas the turbidite layers are level at the sea-floor, they become progressively tilted with depth, more so to the northeast than to the southwest. It can be speculated that this local deformation is due to differential com paction, normal faulting or to disturbances associated with rifting, in turn possibly caused by strike-siip. The evidence for the latter is tenuous. Further, the contacts of the turbidites today with the adjacent trench walls are difficult to ascertain, even along this oblique trench crossing. Three closely adjacent crossings of the Aleutian Trench were made on Lines B-31, B-32 and B-33 (Pis. 6 and 7). On the oceanic side of the trench. Line B-31 shows a thin section of flat, undisturbed turbidites abutting pelaglcs which are obviously older than the turdibites. 148 The middle crossing of the trench (Line B-32) reveals no turbidites or flat floor whatsoever, and the elevation of the trench Is measurably higher than that of the two Im mediately adjacent trench crossings. It is possible that this is the reflection of local uplift. In addition* the reflector which marks the surface of the acoustic base ment seaward of the trench appears to be dipping under the trench for about 7 km. There is some possibility that this is a spurious acoustic return from the south wall* but the likelihood that it is a genuine subbottom is greater. Hence, it is appropriate to make the interpreta tion that slump debris from the Aleutian Ridge has burled pelagic deposits underlying the trench floor. (No buried turbidites are to be seen.) A similar interpreta tion can also be applied to Lines B-44, B-45 and B-47 crossing the Kuril-Kamchatka Trench. The floor of the trench on Line B-33 is flat and undisturbed and the turbidite section appears to be thin. The trench floor is flat on the crossing made by Line B- 36 (FIs. 8 and 9)i the turbidites appear mildly deformed (flexed) with depth. Oceanic acoustic basement is shown to pass under the trench and underlie pelaglcs on the Aleutian side. The turbidite floor on the Line B-37 (Pis. 10 and 11) crossing Is flat and the layers of sediment show only minor deformation with depthj however, a central, down- 149 dropped (keystone) block can easily be envisioned here. Again the turbidites overlie and post-date the pelaglcs of the south wall. The crossing of Line B-38 (Pis* 12 and 13) has al ready been discussed in connection with the trench sedi ments and the sediments of the inner wall. The structures interpreted here, as well as for Line B-37, suggest the idea of oblique pull-apart* a type of extensional rifting which may be related to strike slip. The floor of the Kamchatka Trench is essentially void of turbidite fill which precludes the type of structural analysis applied to the Aleutian Trench, Peninsular and Insular Slopes The south slope of the Aleutian Ridge does not have the same type of major structures discernible from the seismic reflection profiling records along the peninsular slope of Kamchatka. Instead, one finds the slope under lain on virtually all the crossings with deformed rocks of the Early Marine Series. Slumps are common, as are normal faults. Layered sediments in basins are tilted downslope (Line B-30i Pis. 4 and 5) or antithetically (Line B-36f Pis. 8 and 9) and reflect forward or backward rotation of local structural blocks. Large basins, possibly part of the Aleutian Terrace, show multiple episodes of sediment fill, in some cases with intervening tectonic activity 150 (Line B-35, Pis. 6 and 7| Line B-38, Pis. 12 and 13). In all, the structures on the Aleutian Ridge reflect con siderable tectonic activity, both old and recent. The peninsular slope of the Kuril-Kamchatka trench has one set of structures of major Importance. Three of the four transects of the trench show the reflector which marks the surface of the oceanic acoustic basement (Layer 2) passing westward beneath the trench and extending under the Inner wall. In Line B-44 (Pis. 16 and 17) the ship's track Is normal to the trench and the west-dipping re flector can be traced at least 12 km under the peninsular slope. In Line B-45 (Pis. 18 and 19) the situation Is similar except that the reflector appears to be offset In a fashion here interpreted as a minor underthrust or re verse fault. In Line B-45 the surface of oceanic basement can be traced 17 km beneath the inner slope. Line B-47 (Pis. 22 and 23) has posed serious problems In interpretation. A reflector passes under the trench and dips beneath the slope for at least 9 km and possibly as much as 15 km. A shallower reflector also passes under the trench and slope. Projections from these reflectors have been made on the interpretative overlay which result In a picture of the oceanic basement under- thrusting Itself In the process of being thrust under the Kamchatka Peninsular slope. Antithetic normal faulting is also possible and entirely in keeping with the Idea of 151 underthrusting. Structural relationships In this crossing are complicated, but the Interpretation of oceanic base ment passing under the Kamchatka slope Is made with con fidence . The inner trench wall of Line B-44 Is described in Appendix A, but it is worth while to summarize several of its characteristics and to indicate how they might support alternative structural interpretations. The slope is, or was, unstable. This is testified to by a back-rotated block high up on the slope with shoreward dipping layered sediments covered with flat sediments in the basin formed by the back rotation. Additional normal faults are seen farther down the slope. Adjacent to the trench proper, the inner trench wall is a highly convoluted, irregularly surfaced slope, which could be slumped material, EMS or LMS of the Kamchatka Terrace, or highly deformed pelagic debris. In the latter instance the material could be considered pelagic off-scrapings and this is the preferred interpretation shown on Plate 17. A third alternative is that the material over the basement reflector is both pelagic and slumped material, the latter covering, or mixed with, the former. The slumped material (?) lacks coherent internal reflectors which tells one only that, if it is sediment, it is probably highly deformed. The inner trench wall on Line B-45 (the section be tween the trench proper and the outer rampart of the Kam 152 chatka Terrace (see Pis. 18 and 19) also has a highly convoluted surface with back slopes which could be inter preted as slumps. Like Line B-44, an oceanic basement reflector is confidently interpreted to pass under the inner trench wall. It is even shown to be reverse fault ed, although an east-dipping normal fault could just as well have been drawn (see p. B-45-7), A possible static model for trench formation is sketched on Plate 19, but this does not account for the shoreward dipping basement reflector. The sediment of the inner trench wall, near to the trench, can only be said with confidence to be deformed. Most of the general comments made In the previous paragraphs about Line B-44 also apply to Line B-45. On Line B-46, the inner trench wall has the same rolling, irregular surface as B-44 and B-45. Its average slope is 4°30'. Sediment beneath this wall is totally devoid of internal reflectors and has the same aspect of deformed sediment as B-44 and B-45. A section of steep and smooth sea-floor at the top of the slope suggests a slip surface. This could be the original position of material which has slumped to a lower posi tion. Several minor reverse slopes suggest the same relationship. Notable is the lack of a reflector showing the top of oceanic basement dipping shoreward under the inner trench wall (as compared with the other three cross- 153 ings of the Kuril-Kamchatka Trench). The record of Line B-47 compares with the preced ing lines in that the part of the inner wall adjacent to the trench proper has the same type of distinctive sea- floor topography. The upper part of the inner wall is steep* with a calculated slope of 10°42,« It is smooth and highly reflective and a large slump was suggested earlier to explain the mound at its base. Sediments im mediately adjacent to the trench* and directly under it. have the general aspect of distorted sediment which could have covered an old trench. But the same reasoning ap plies to offscraped pelagic sediments which the shoreward- dipping basement reflectors favor. Thus* the evidence of the records alone* unin fluenced by knowledge of a Benioff zone passing under Kamchatka* seismic activity and other elements of the New Global Tectonics* permits a simple interpretation (Fig. 9) of gravity slumps to explain the relations shown in the records of Lines B-44, B-45, B-46 and B-47. Slumping is not, however, the preferred interpretation* even admitting the extreme difficulty of moving soft pelagic sediments some tens of kilometers up a substantial slope. Figure 9. Diagrams to illustrate how oceanic subbottom reflectors could be found under the trench inner trails with out appealing to subduction. In the upper diagram* A* a trench formed by some other means than underthrusting is shown. The type of mechanism is not important. In the lower diagram* B, part of the inner trench wall has slumped down and buried the old trench* forming a new trench farther seaward. The old oceanic pelagic layer and acoustic basement remain where they were* but are now covered* with their boundaries plunging under the inner wall of the new trench. 154 155 DISCUSSION AND CONCLUSIONS General The basic objectives of this investigation were to seek and evaluate evidence, either structural or sedi- mentological, bearing on the Interaction of the Faciflc plate with the Eurasian plate and the American plate and on the problem of the Eurasian-North American plate boundary in the area of the convergence. If the New Global Tectonics is accepted, then one also accepts rela tive movement between the plates. The basic questions then arisei (1) what was (or is) the relative direction of movement of the Pacific plate with respect to the Eurasian-North American place, (2) what was the amount and rate of movement, (3) when did the movement take place, (4) was the movement continuous, periodic, or episodic, and (5) what is the structural nature of the boundaries? The evidence adduced in this study is straight forward and relatively simple to apply to the problem. Before this is undertaken, however, it is appropriate to briefly describe and discuss the selection of models available which pertain to plate motion in the North Pacific. 156 157 Models for Plate Movement In the North Pacific Continuous Motion Model Atwater (1970) and Grow and Atwater (1970) analyz ed magnetic anomaly patterns in the northeast Pacific and* making certain assumptions regarding the integrity and unity of the Pacific plate and the general validity of the plate tectonic hypothesis, synthesized a model of plate motion primarily for the Cenozoic but with implica tions as far back as the late Mesozoic. Some of the basic elements of the model arei 1. A mid-Cenozoic, northwest trending trench existed off western North America. 2. A mid-ocean spreading center (East Pacific Rise) trending north and south and offset by transform faults (the great fracture zones such as the Mendocino and the Murray (Menard, 1964), separated the Pacific plate to the west from the Farallon plate (McKenzie and Morgan, 1969) to the east. 3. The trench separated the Farallon plate to the west from the American plate to the east. 4. With the Pacific plate fixed relative to the Farollon plate, both the Farallon plate and the spreading center migrated easterly and were subducted in the trench. The relative rate of motion is estimated at 7-10 cm/yr. 5. The initial cessation of trench activity and 158 subductIon (as determined by the age of the youngest anomalies in the Pacific plate where they meet the con tinental margin of the United States) is approximately 30 m.y. ago (upper Oligocene per Berggren, 1972). 6. The northwest-southwest trending San Andreas system may have begun movement (right lateral) at this time (30 m.y. B.P.). 7. The American plate has been moving with re spect to the Pacific plate at the rate of 6 cm/yr for at least the past 4-5 m.y., and perhaps for as long as 30 m.y, 8. The Pacific plate and Farallon plate were separated from a late Mesozoic plate to the north (Kula plate of Grow and Atwater* 1970) by an east-west trending spreading center. With the Pacific plate fixed relative to the Kula plate, both the Kula plate and the Kula spreading center migrated in a north-northwest direction and were subducted by the Aleutian Trench. 9. The net motion of the Pacific plate has been constant and to the northwest approximately parallel to the present strike of San Andreas Fault. This plate movement at present is relative to the American plate and about a pole of relative motion at latitude 53° N, longi tude 53° W off Labrador (Morgan, 1968). The Pacific plate has maintained a velocity of 6 cm/yr since at least middle Oligocene (30 m.y. B.P.). Atwater (1970) offers 159 two possibilities with regard to the relative notion dur ing the first 26 m.y. of the 30 m.y. periodi (1) all the accommodation has been made by the San Andreas Fault In conjunction with a complicated sequence of shifting plate boundaries and migrating triple Junctions along the western margin of the American plate, or (2) the Pacific and American plates were locked together until about 5 m.y. B.P. When they broke apart and relative movement between them began to take place along the San Andreas. Atwater's (1970) preferred model appears to be the one which has 30 m.y. of continuous relative motion along the San Andreas (labeled as inescapable) preceded by rela tive motion between the Pacific plate and the North Ameri can plate of 6 cm/yr back 80 m.y. B.P. (late Cretaceous) to suggest an overall travel of the Pacific plate of 4800 km since 80 m.y. B.P. (late Cretaceous). It is interest ing to note that Larson and Chase (1972) also suggest a comparable amount of northerly motion of the Pacific plate (4500 km) to account for the difference between the present position and the position of formation of magnetic anomaly patterns located in the western equatorial Pacific. They have inferred that this motion has taken place since 120 m.y. B.P. (Cretaceous). Heezen and others (1973) have constructed a model of motion for the Pacific plate based on the deposition of pelagic sediment units on a growing western Pacific 160 crust* The key appears to be the presumption that pelagic sedimentary sequences of the Pacific are time transgres- slve and that the varying age of the contact between an upper layer of unllthlfled brown clay (20-100 m thick) and an underlying thicker (300 m) sequence of chalk* chert and clay can be used to date the amount and direction of plate movement. The scheme Is Interesting but not especially rigorous. The authors conclude that the Pacific plate has moved with a northerly component at the rate of 4.4 cm/yr from 100 m.y. (Cretaceous) to 30 m.y. (middle Oligocene) B.P. and at 2 cm/yr from 30 m.y. B.P. to the present. The movement of the Pacific plate is considered to be to the northwest (310° T). Thus Heezen and others (1973) are invoking a total movement In this direction of 3329 km at an average rate of 3.3 cm/yr. Discontinuous Motion Model Pitman and Hayes (1968) proposed a model for ex plaining the motions of the Pacific plate in relation to the American plate which also accounts for the bend in magnetic anomalies in the Gulf of Alaska which has come to be called "The Great Magnetic Bight*1 (Elvers and others* 1967). This model was later revised and refined (Hayes and Pitman* 1970)* but the basic ideas remain the same. The principal elements of this model include the following! 161 1. A triple Junction of spreading ridges existed south of the Alaska Peninsula in the Cretaceoust one ridge trended east-west at a position south of what Is presently the Aleutian Arc. one ridge (the East Pacific Rise) trended south-easterly and southerly, and one trended northeasterly and northerly. All were offset by transform faults. 2. Four plates were evident* a. A relatively-fixed Pacific plate bordered on the north by the east-west spreading ridge and on the east by the southeasterly-southerly spreading ridge. b. A mobile plate north of the east-west ridge, but south of a trench which was approximately in the position of the present Aleutian trench. c. A fixed North American plate east of a trench bordering western Canada and also north of the "Aleutian** trench, and d. A mobile plate (Farallon plate) between the trench bordering western Canada and the northeasterly- northerly and southeasterly-southerly ridge axes of the triple Junction. 3. Pitman and Hayes (1968) suggested that spread ing took place along the east-west ridge axis against a relatively fixed Pacific plate and that the mobile plate and spreading center both migrated northward and disappear ed down the Benioff zone of the "Aleutian** trench. The 162 north-south spreading stopped when the east-west spreading axis and the plate north of it were subducted. At this time the trench became quiescent and north-south movement ceased. The time of this event, as suggested by magnetic anomalies running into the trench, was early Paleocene (65 m.y. B.P.). 4, The mobile plate between western Canada and the other two spreading axes of the triple junction, also migrating away from the relatively fixed Pacific plate, continued their easterly movement until they were sub ducted down the trench along the western Canadian margin. This activity finally terminated in early Pliocene (5.0 ra.y. B.P.). A consensus of several investigations (e.g., Stauder, 1968a,bi LePichon, 1968i Morgan, 1968i 1sacks and others, 1968i Oliver and others, 1969\ Grow and Atwater, 19701 Atwater, 1970% Cormier, 19721 and many others) has adduced, primarily on the basis of first-motion earthquake mechanism studies, that the Pacific plate is presently moving northwesterly and that subduction is taking place in the eastern and central portions of the Aleutian Trench. Pitman and Hayes (1968) and Hayes and Pitman (1970) proposed that this movement began in the Pliocene, caused the present-day Aleutian Trench, and resulted from a change in direction of motion of the Pacific plate. Their model precludes significant motion of the Pacific plate 163 from early Paleocene to the Pliocene and also Implies that the present Aleutian Trench was formed in the Plio cene as a result of the inception of movement of the Pacific plate at that time. Models of Little or Wo Motion Some investigators do not feel that it is necessary to appeal to hypotheses requiring plate movement over the thousands of kilometers preferred by Atwater (1970) to ex plain the observed interrelations of trenches* magnetic anomalies, spreading ridges and sediment distribution patterns. In their models they advocate that movement even over relatively short distances (a few hundreds of kilometers), while not precluded* is also not a require ment. Examples are given below. Hamilton*s Modelsi A study by Hamilton (1967) of the fossil Aleutian Abyssal plain (located in the Gulf of Alaska south of the Alaskan panhandle and the eastern Aleutian Islands directly over the Great Magnetic Bight) concluded that the cessation of turbldite sedimentation which formed the plain occurred at the time of formation of the Aleutian Trench. The argument which provided the basis for this was that the source of turbldltes was on the continental side of the trench locale* and that the trench, as it formed* would have trapped turbidity cur rents that otherwise would have flowed south to the 164 Aleutian Abyssal Plain. A section of pelagic sediments overlies the turbldltes. Hamilton (1967) logically as sumed that the onset of pelagic sedimentation marked the cessation of turbldlte sedimentation and, therefore, the time of formation of the Aleutian Trench. He applied several sedimentation rates to the maximum measured thick ness of pelaglcs overlying the turbldltes (on the western side of the plain) to determine the age. Using rates of 1 m/1000 years, 2 mm/1000 years and 5 ram/1000 years, a possible range in age from Upper Cretaceous to middle Miocene was adduced. Hamilton's preferred rate was 2 mm/1000 years, resulting in his opinion that the probable age for initiation of pelagic sedimentation and formation of the Aleutian Trench was middle Eocene (48 m.y. B.P.). JOIDES Hole #183, drilled in the northwest Aleutian Plain near Seamap Channel, penetrated the pelaglcs and the turbldltes. The range of dates determined on the turbld ltes was mid-Oligocene to early late Eocene (Scholl and Creager, 1973). This was a remarkable confirmation of Hamilton's prediction. Since the 1967 paper, Hamilton gathered additional new data on the Aleutian Abyssal Plain, as have Mammerlckx (1970), Naugler (1970) and Jones and others (1971). Recently Hamilton (1973) enlarged and refined his original investigation of the Aleutian Abyssal Plain and documented Its significance with regard to plate tectonics In the 165 northeast Pacific* He concluded that* 1. The fossil turbidite Aleutian Abyssal Plain was formed at, or very near, its present position in Eocene-Oligocene time. 2. The source of the sediment was Alaska, probably the Cretaceous flysch of the continental terrace south of the Alaska Peninsula. 3. Paleoclimatological evidence argues for little to no northward plate movementi lack of required amounts of trench sediment off-scrapings argue against large amounts of northerly plate movement as do the undisturbed trench floor sediments. 4. Spreading models precluding deposition of the Aleutian Abyssal Plain in approximately its present posi tion are not acceptable} the same applies for models in voking an actively subducting Paleogene Aleutian Trench. Embracing this Idea essentially eliminates the Kula plate concept. 5. Plate movement is not necessary to his models but a small amount can be accepted. Hamilton (1973) reasoned that two models are con sistent with the datai 1. A discontinuous spreading model with episodic subduction somewhat similar to that of Pitman and Hayes (1968)j the basic difference is that the modem Aleutian Trench would have been formed in the middle Oligocene 166 rather than in Pliocene, and that the trench was maintain ed without a large northward movement of the Pacific plate (the model permits 240 km of north-northwest move ment of the Aleutian Abyssal Plain in the last 4 m.y.). 2, A non--or very little--spreading model. Ihis model permits a small amount of spreading but does not require it. Hamilton does not express a preference for either of these two models. Either poses serious questions for the continuous movement, long travel models. Scholl and Creager (1973) suggested a similar model but see little reason to call for an Oligocene trench. Instead they relate cessation of turbldlte sedi mentation to a major onshore reorganization of principal drainage routes and the formation of large marginal basins. Marlow and others (1973a) also proposed a discontinuous model based on the formation of the central Aleutian Ridge. Peter's Static Modeli Geophysical studies reported by Peter (1965, 1966) and Peter and others (1965, 1970) provided the basis for presenting a model which is es sentially static and calls for the Aleutian Trench to have been formed as a result of downfaulting or downbow ing of oceanic crust rather than by crustal underthrusting (Peter and others, 1970). Without crustal underthrusting the plate tectonic hypothesis is not viable unless the 167 earth is expanding. Peter's model is argued on the basis of the follow ing points t 1. Magnetic anomalies cross the trench from oceanic crust and extend over the Aleutian Terrace. If the oceanic crust were subducted down the fieinoff Zone the magnetic anomalies would have been erased. (This argument is in direct contrast to Silver's (1969) report that magnetic anomalies, five million years old, can be traced under the continental slope of northern California, and that this constitutes evidence for underthrusting.) 2. Magnetic anomalies intersecting north-south trending fracture zones (Amlia and Adak) have reduced amplitudes to the west of the intersection. Also, these fracture zones have no obvious topographic expression. According to Peter and others (1970), both these phenomena indicate that the features are associated with an independent formation of the trench rather than with a subducting Pacific plate. 3. The pattern of magnetic lineations and north- south trending fracture zones observable is at odds with the type of pattern that theoretically should develop with the compressIona1 interaction of an arcuate ridge and a rigid underthrust plate, both part of a convection system. The authors reason that if the oceanic crust migrated into an arcuate trench, the magnetic anomalies 168 south of the trench would also have to be arcuate, general ly conforming to the shape of the trench. Fracture structures should be radial to the arc. The observed magnetic anomaly lineations near the Aleutian Trench are east-west and straight and the fracture zones are north- south and not in a radial configuration. 4. Negative isostatic anomalies are noted in as sociation with trenches. Advocates of compressive rela tions (underthrusting) believe that rapid compensation of the "static mass unbalance" is precluded by the continuing dynamic force of a downgoing plate. However, in agreement with Shor (1966), Peter and others (1970) support a tensional regime where the trench is formed as a direct outgrowth of formation of the ridge on oceanic crust. In this scheme the island arc, trench and outer ridge systems interact mutually. The negative isostatic anomaly at the trench is attributed to the elastic behavior of the crust. 5. If the sea floor moved north, topography on the outer ridge of the trench should be transported into the trencht such is not the case for the high relief of the outer ridge does not continue on to the south wall of the trench (Peter, 1970). 6. Trenches and continental margins are magneti cally quiet because downbowing or downfsuiting of the crust may carry it to a depth where temperature may erase the magnetization. 169 7, Most models of crustal underthrustingt whether continuous or discontinuous, note that the trend of the western Aleutian Trench is parallel to the direction of movement of the Pacific plate (e.g., Isacks and others, 1968) and that the relations are strike slip. They also include formation of the trench by plate movement at what ever time. If the isostatic unbalance of the trench were the result of continuing crustal underthrusting, the west ern Aleutian Trench should have compensated, or shown some sign of compensation, since underthrusting ceased. The western Aleutian Trench appears to be as well-developed as the remainder of the trench and there is no evidence of elastic reboundi there appear to be no significant dif ferences between the part of the trench that is strike slip and the part that is allegedly underthrust. Thus, a compresslonal origin for trench formation is suspect. It is obvious that Peter and others (1970) be lieved that the preponderance of evidence points toward a trench origin which does not involve convection, conver gence, subduction or plate travel. Emergence Model Not all students of the mobile tectonics of the northeast Pacific subscribe to the concept that movement of the crustal plates or the sea-floor is northward toward the Aleutian Trench. Perry (1969, 1970, 1971) was im pressed that magnetic anomalies paralleling the Aleutian 170 Trench In the Gulf of Alaska Increased in age to the south starting with a Cretaceous-Paleocene age at the trench proper. As previously mentioned, these anomalies are attributed by both Hayes and Pitman (1970) and At water (1970) to the activity of a northward migrating spreading ridge now subducted. They are the residual imprint, the relict signature, of the Kula spreading ridge (Atwater and Grow, 1970). Perry (1971) was further impressed that sediments in the present-day trench are essentially undisturbed, a condition which is not in harmony with the idea of subduction, at least concurrent subduction. This observation also has been made for the Peru-Chlle Trench by Scholl and others (1968). Based on these two conditions, on further Interpretations of earth quake mechanism tension and compressional phenomena beneath the Aleutian Arc and the Pacific sea-floor, and on bathy metric and structural information, Perry (1969, 1970, 1971) proposed what he termed an emergence model to explain the situation. The basic elements of the emergence model are> 1. Sometime in the Mesozoic a subdued ancestral Aleutian ridge existed at the approximate locale of the present Aleutian Arc and developed new crust which spread to the south (following the general precepts of the plate tectonic hypothesis). 2. Magnetic llneatlons, now seen parallel to and south of the ridge, are the result of this spreading. 171 3. Spreading stopped in Paleocene* 4. After spreading ceased* the present Aleutian Ridge was formed by accretion of volcanogenlc material and by uplift along a normal fault which borders the northern side of the ridge. 5. The dominant relation between the Aleutian Ridge and the Pacific plate Is extension. This Is In contrast to the relations of compression and convergence for all other spreading models. Tenslonal earthquake phenomena are attributed to separation of the ridge and the Pacific plate in contrast to the opposite view that tenslonal phenomena result from the bending along the top of a subducting Pacific plate. Compressions! earthquake phenomena are explained as the result of shear occurring when the base of the Aleutian Ridge rises faster than the underlying mantle In contrast to the idea that the com pressive phenomena result from an underthrust plate. 6. The Aleutian Trench formed as the result of tension during a Pliocene orogeny. It has dropped as a result of raonoclinal bending along its southern (oceanic) margin and normal faulting along its north wall. There was neither horizontal motion along the trench during its formation nor has there been any since. 7. The Aleutian Terrace Is* likewise* a tenslonal feature which began to form in the Pliocene. Perry (1971) considered it to be a rift which today is still opening 172 faster than It can be filled with sediment emanating from the ridge. Perry's model Is regarded with considerable curiosity, primarily because It stands In stark contrast to the other models. Discussion of Models and Sedimentation In appraising the models of plate motion Just dis cussed, the evidence adduced from the seismic reflection records and from the data on sedimentation were examined against the backdrop of the New Global Tectonics for the answer to simple questions. First, which models have elements In such basic disagreement with either the observed facts and preferred Interpretations or the acceptable tenets of the New Global Tectonics that they need no longer be considered? Perry's emergence model Is obviously in this cate gory. It essentially denies the basic elements of the New Global Tectonics, substitutes source for sink, reverses the direction of crustal plate motion, Invokes tension rather than compression for the relations between the Pacific plate and the Aleutian Ridge, and gives alterna tive Interpretation to focal mechanisms. In a word, It Is In total disharmony with the New Global Tectonics and Incompatible with much of the well-established geologic data. 173 The static model of Peter and others (1970) Is considered an excellent model for the data on which It Is based and would be difficult to disprove, but It Invokes down-faultIng or downbowlng of oceanic crust rather than underthrusting to create the Aleutian Trench. This Is in direct antithesis to the New Global Tectonics. Further, Peter and others (1970) Interpret magnetic anomalies and fracture zones just south of the Aleutian Trench to be in conflict with patterns that should result from compressive interaction of an arcuate ridge and an underthrust plate. Thus» it also is disharmonious with the New Global Tectonics and with the well-documented body of seismic, petrologic, magnetic and geologic data which establish the New Global Tectonics as a viable working hypothesis. Thus it can also be omitted from further discussion. There remain the models of continuous motion, models of discontinuous motion, models of little motion, and models of no motion which do not preclude motion. None of the new data presented here permit an im provement In determining the direction of motion of the Pacific plate. The direction is northwesterly and close to being normal to the trend of the Kuril-Kamchatka Trench) this is in accord with the conclusions of a large number of students of the problem (Stauder, 1968a,bj Le Plchon, 1968) Morgan, 1968) Oliver and others, 1969) Grow and Atwater, 1970) Atwater, 1970) and Cormier, 1972). If 174 the plate is in strlke-sllp relation with the North American plate, the direction is approximately 305° T which is the trend of the far western Aleutian Trench. The boundaries of the Pacific plate in the study area are the two converging trenches. In the models where any spreading and subduction are permitted, the Kuril- Kamchatka Trench would be considered a normal boundary. The preferred interpretations of the crossings of the western Aleutian Trench and the adjoining seaward wall of the Aleutian Ridge show essentially no structures com parable to the combination of down-dipping basement and possible pelagic offserapings shown in the transects of the Kuril and Kamchatka Trench. The interpretation of massive slumps from the Kamchatka slope covering an old trench and forming a new one farther to sea is considered a less desirable alternative. One line across the Aleutian Trench (Line B-32, Pis. 6 and 7) has a subbottom reflector trending under the ridge in an area where there are no turbldltes on the trench floor, and this is a pos sible exception where slumps from the Aleutian Ridge may have reached the trench floor. Other Interpretations (see below) of this crossing also are possible. A series of conditions are observed in the Aleutian Trench which make sense if one compares them with the general characteristics of a rift zone. For example, bodies of rock material interpreted as oceanic pelaglcs 175 with underlyIns oceanic basement are present at the foot of the Aleutian Kidge (Lines B-36 and B-38P Pis. 8, 9, 12 and 13* possibly, also* on Line B-37, Pis. 10 and 11) separated from the oceanic sea-floor by the flat turbld ltes of the trench floor. The bodies appear to be topo graphically unrelated to the ridge. On Line 38 (Pis. 12 and 13) secondary turbldlte channels are separated by small topographic highs which also are Interpreted as small slices of oceanic pelaglcst the channels are measurably higher than the adjacent trench floors. Lines B-31, B-32, and B-33 (Pis. 6 and 7) all cross the trench In close proximity. Lines B-31 and B-33 show well- developed turbldltes whereas Line B-32 shows none. The maximum depth on the Line B-32 crossing Is measurably higher than the other two. This suggests uplift or relative vertical movement. Altogether the Impression Is one of extenslonal rifting with local vertical movement. The rifting could be the outgrowth or result of strike slip relations In the area of the ridge and trench. The evidence is suggestive and corroborative rather than definitive. Thus, the geological and geophysical data, as Interpreted in this research, support the concept that the far western Aleutian Trench is a zone of local extension or rifting, possibly related to strlke-sllp motion parallel to the ridge. Accepting the idea of strlke-sllp 176 relations between the North American and the Pacific plate, the western Aleutian plate boundary can be des cribed as a trench-trench transform fault as suggested by Grow and Atwater (1970). The amount and rate of movement of the Pacific plate can be approximated by a study of the massive de posits of pelagic and hemlpelaglc sediment delineated on the acoustic basement south of the trench convergence area. This section comprises up to 1.5 km of material which is terrigenous and blogenous (pelagic) in character. The age and nature of the sediment and its rate of deposition are accurately known from drill data of JOIDES hole 192 which Is almost directly on Line B-43. The average rate of deposition from the late Cretaceous (minimum age of the acoustic basement) is more than an order of magnitude larger than established rates for pelagic deposition in the deep sea at distances far from land. Opdyke and Foster (1970, Fig. 20) plotted sedi mentation rates in the Pacific for the Brunhes epoch (0.7 m.y. B.P.) and presented boundaries for sedimentation rates of 3 mm/1000 years and 12 mm/1000 years. The nearest position to the site of JOIDES 192 where a sedimentation rate of 12 mm/1000 years could be is approximately lati tude 46° N, longitude 177°30' E which is about 1170 km distant. This boundary serves as a basis for speculation on the amount of plate movement based on sedimentation 177 rates. Atwater's (1970) model calls for 6 cm/yr of travel of the Pacific plate relative to the North American plate along the west coast of the United States since at least mid-Oligocene (30 m.y. B.P.). The movement is about a pole of rotation at latitude 53° N* longitude 53° W. The motion is northwest* and in the Meijl area the rate would be at least 8 cm/year. This amounts to about 1200 km since the early middle Miocene (15 m.y.). By this reason ing the JOIDES site would have been 1200 km (648 nautical miles) to the southeast at approximate latitude 47°30' N. longitude 177°30* E during the early middle Miocene* when the sedimentation rates at this site were greatly ac celerated by the Infall of terrigenous debris. If the sediment thicknesses shown on the chart of Opdyke and Foster (1970) are related to sedimentation rates as far as directions of Increase or decrease are concerned* then a projected sedimentation rate at this position (latitude 47°30' N, longitude 177°30* E) in the early middle Miocene is probably a little larger than the 12 mm/1000 year con tour which is slightly to the southeast. A rate of 15 mm/1000 years is considered a conservative figure, es pecially because sedimentation rates for the Brunhes are high compared to the rest of the Neogene in this area (D. W. Scholl, personal communication). Yet the conserva tive calculated sedimentation rate from JOIDES 192 for the 178 middle Miocene Is 39 ram/1000 years more than twice as much. And this does not take compaction into account. If the section approximately 7 km to the north-northeast of JOIDES 192 (see Line B-43) had been used, an increase factor of 1.6 could be applied giving a rate of 62 rom/1000 years for the middle Miocene. These figures can be juggled but if the assumptions are correct or even ap proximately correct, then it is difficult to escape the conclusion that the JOIDES 192 site was not at latitude 47°30' N, longitude 177°30' E during the early middle Miocene, or anywhere near that position. Rather it must have been close to Kamchatka and terrestrial sources of sediment which could have produced the high rates of sedimentation measured. The portion of Kamchatka near the convergence area designated as the prime sediment source is abetted by the distribution of sediment thickness in the "arrowhead** area. Examination of Figure 7 shows that the section of pelaglcs and heraipelaglcs lies like a long tongue with its root at the trench convergence south of Kamchatka Pass. The pattern is complicated by the Emperor Seamounts Chain and is thus not symmetrical, but it is simple, the thick est part of the section being at the convergence with thinning occurring both to the southeast and the south west. This demonstrates that the bulk of the material came from Kamchatka proper or from the Kamchatka Basin of 179 the Bering Sea by way of the Kamchatka Pass. There la no Indication that any substantial amount of sediment was contributed from the Aleutian Ridge. It does not have a large, land area compared to Kamchatkai in addition the "terrace" basins and trench would have probably trapped whatever sediment was produced* Envistoning this tongue of sediment 1200 km to the southeast raises difficult questions. The distal end of the tongue, presently below Attu, would be at longitude 175° W and approximately 780 km south of the Aleutian Ridge. What was the sediment source? Certainly not the continental sources to the southeast. They are too dis tant, and would not thicken with increasing distance from the source. The pattern precludes the Aleutian Ridge, as does the restricted source area of the Aleutian Ridge. The thicknesses are too excessive to consider pelagic sources alone. This leaves the preferred interpretation that the tongue of sediment is presently very close to the site of its original deposition. Thus, the continuous motion model of Atwater (1970) is not considered appropriate to the data. Remaining are the discontinuous motion model of Hayes and Pitman (1970) which permits Neogene spreading only since the Pliocene and the discontinuous spreading models of Hamilton (1973), Scholl and Creager (1973), and Marlow and others (1973a) which allow a few hundred kilometers of north-northwest 180 plate movement. Either Is consistent with the data of this report. Because some plate movement is necessary to produce the offscrapings and underthrust acoustic base ment (which Is the writer's favored interpretation), a few hundred kilometers sometime since middle Miocene seems a reasonable figure to accept. Data to give this greater precision are not available. Whether the movement was episodic, periodic, or continuous during this period is moot. Conclusions on Plate Motion The evidence with regard to plate motion and boundaries in the convergence indicates thati 1. The Pacific plate is being subducted in the Kuril-Kamchatka Trench* the western Aleutian Trench is an extenslonal rift boundary possibly associated with strlke- sllp* lack of trench sediment deformation suggests the main zone of slip may be under the Aleutian Ridge as sug gested by Cormier (1972). 2. As Judged by sedimentologleal evidence the Pacific plate has probably moved no more than a few hundred kilometers since the early middle Miocene. 3. The direction of motion of the plate is north west, probably parallel to the azimuth of the far western Aleutian Trench (305° T). 4. The data are in agreement with the models of 181 plate movement In the northwest Pacific of Hayes and Pit* man (1970), Hamilton (1973), Marlow and others (1973) and Scholl and Creager (1973). The North American*Eurasian Plate Boundary The Problem The New Global Tectonics specifies that plate boundaries are either spreading centers, subduction zones (trenches or young folded mountains) or transform faults. These features are delineated primarily by bathymetric (topographic), seismic, heat flow, and paleomagnetic determinations or by the abrupt termination of major geologic features or structural trends. The margin of the North American plate has rela tively clear-cut boundaries in the Alaska-Bering Sea area as far as the Pacific plate to the south is concerned— the Aleutian Trench. The Kamchatka Trench marks the edge of a plate also, and according to early students of the New Global Tectonics this was the Eurasian plate. Thus it was tempting to continue the Kuril-Kamchatka lineament north ward* forming a triple Junction at the trench convergence, and a boundary between the North American plate and the Eurasian plate in the Bering Sea. Indeed, some of the early charts (Isacks and others, 1968, Fig, 2j LePichon, 182 1968, Fig. 6) show the boundary crossing the Shlrshov Ridge and passing through the Bering Strait Into the Arctic Ocean. Morgan (1968, Fig. 1) shows Kamchatka and eastern Siberia to be part of the North American plate with the boundary extending out of the Arctic at about longitude 140° E, trending through the Japanese Islands of Sakhalin and Hokkaido and forming a triple Junction at the Juncture of the Japan-Kuril-Kamchatka Trenches. This also appears to be the view of Dewey (1972) who has an "uncer tain” boundary so drawn.(see Fig. 1). Still others merely ignore the problem and show no boundary whatsoever. Churkin (1968) addressed himself to this problem and pro posed that the boundary extends south from the Gakkel Ridge in the Arctic Ocean, down through the region of Yakutia in eastern Siberia, and Joins the Pacific plate boundary at some vague position near south Kamchatka. Although a growing amount of evidence indicates that the margin does not go through the Kamchatka Basin and the Bering Strait, a clear-cut identification of the boundary remains a problem. The records of the 1970 ex pedition were studied to see if any pertinent evidence could be found. Evidence No direct, positive evidence was developed from the seismic reflection profiling records which could be 183 considered applicable to the problem. However* informa tion indirectly bearing chi the problem was discovered in the course of the study* namelyi 1. When the broad outlines of the geology and stratigraphy of the Near Islands and the Komandorsklye Is lands In the Aleutians are compared with those of eastern Kamchatka and the northern Kurils* a correlation of events* especially a mid-late Miocene orogeny* is noted. This is not compelling evidence, but is suggestive that all the areas were part of the same geologic province. 2. Russian geologists are in almost total accord with the idea that the Komandorsklye Islands are closely related to Kamchatka and are a portion of the same geologic province. These relations were discussed in the text and includet a. A possible land bridge between Bering Is land and Kamchatka (Udintsev* 1955). b. A direct connection between the Komandor- skiyes and Kamchatka as recently as the end of the Pleistocene (Vasil*yev, 1957). c. Paleobotanlcal affinities between the two areas (this is not considered to be strong evidence) (Zhegalov* 1964). d. Petrological and mineralogies1 affinities between both the sedimentary and igneous rocks of the Komandorsklye Island and Cape Kamchatskly (Zhegalov, 184 1964) suggest a common source. This Is a fairly good argument and is In accord with Churkins (1968) account of the association of llthologies between western Alaska and eastern Siberia In the latitude of the Bering Strait. Conclusion This information is suggestive and corroborative rather than definitive, but it reinforces the tenet that far-eastern Siberia, Kamchatka, and perhaps the northern Kurils are part of the American plate and that the boundary between the North American plate and the Eurasian plate extends down somewhere through eastern Siberia and the Okhotsk Sea much as suggested by Churkin (1968). Unsolved Problems The area of the trench convergence is so poorly studied, especially the western Aleutian Trench, that it would be possible to list any number of specific problems which could be attacked with profit. Two are especially worthy of note. Western Aleutian Trench Having concluded that the western portion of the Aleutian Trench is probably strike-slip in nature, one can ask the question which is posed, but not directly stated, by Peter and others (1970)i Why does a trench exist here 185 at all? Trenches are presumed to come about either as a result of subduction when two plates impinge on each other, as the result of vertical tectonics following the classic tectogene concept, or by vertical loading on an adjacent mass. If one assumes that the western Aleutian Trench was formed at some time in the remote geologic past by an impinging Pacific llthospheric plate that has since changed direction, then the constant frictional force of a subducting plate, which forms and maintains the trench, is removed. Thus, the isostatlc Imbalance pre served by subduction should have been compensated long ago, and the trench should have lost its topographic expression either by rebound of the depressed trench, by sedimentary infilling, or by both. Yet the trench maintains its identity and a relatively consistent cross-section through out its entire length, including that portion where direct impingement no longer occurs. Ancillary questions arise also. One has to do with the transition between the strike-slip zone and the sub duction zone. What is the nature of this structurally? Does the underthrust gradually steepen into a vertical zone? Is the transition zone completely different from either the strike-slip or the underthrust--a chaotic melange? The complexity of this relationship is under lined by the data of Cormier (1972) who identified from focal mechanisms (1) strike-slip motion along the northern 186 side of the Komandorsktyes and (2) shearing motion along a penehorlzontal plane on the southern side. The fact that the trench does maintain Its topo graphic Identity at the same time as it exhibits phenomena interpretable as the result of strike-slip activity sug gests that the direction of movement of the Pacific plate may be almost, but not quite, parallel to the trend of the trench and that a small component of movement of the plate under the trench may persist. Is this enough to preserve the trench? If the component of motion is slightly away from the trench, extensional rifting could result. There is little direct evidence from the seismic reflection records that the trench area has severely de formed pelagic or turbidite deposits yet a rift, or trench, has formed. Empty Kamchatka Trench Another enigma is the lack of turbidite fill in the northern part of the Kuril-Kamchatka Trench. With terrestrial sources of sedimentary material far more extensive than the Aleutian Ridge, it should show the same flat floor that the Aleutian Trench does. The large basins interpreted as sediment traps certainly detain a large amount of material which eventually would have been deposited in the trench. However, the bathymetry of these basins indicates that they are not closed, but drain to- 187 ward the trenches. In addition, one would think that the most seismically active peninsular slope in the world (Kamchatka) could dislodge an occasional turbidity flow-- enough to show a little layering in the trench. The four crossings of the trench documented in this study may have fortuitously crossed anomalous areas similar to the Line B-32 crossing of the Aleutian Trench, but this is not, really, probable. 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M. , fi^., "Geologiya SSSR, TOM XXXI, Kamchatka, Kurilskiye 1 Komandorsklye ostrova. Chast'I. Geologicheskoye opisanlye." Izadatel'stvo "Nedra," Moscow. (Geology of the USSR, v. 31, Kamchatka, Kuril and Komandorsklye Is lands, Part I, Geological Description, NASA trans lation TT F-ll, 529, Vlasov, G. M. and Klenov, Ye. P., 1964, Kamchatka* The history of geological development* Chap. VIII, p. 529-547, jjj Vlasov, G. M., fid., "Geologiya SSSR, TOM XXXI, Kamchatka, Kurilsklye 1 Komandorsklye ostrova. Chast'I. Geologicheskoye opisanlye" Izadatel'stvo "Nedra," Moscow. (Geology of the USSR, v. 31, Kamchatka, Kuril and Komandorsklye Islands, Part I, Geological Description, NASA translation TT F-ll, 529. 204 Vlasov* G. M. * Maroz* I. F.* Klenov* Ye. P. and Svyat- lovskly* A. Ye.* 1964* Kamchatkat Tectonlcsi Chap. VI, p. 429-502* iQ Vlasov* G. M.* fid., "Geologiya SSSR, TOM XXXI* Kamchatka, Kurilsklye 1 Komandorsklye ostrova. Chast'I. Gedoglcheskoye opisanlye" Izadatel'stvo "Nedra," Moscow. (Geology of the USSR* v. 31* Kamchatka, Kuril and Komandorsklye Islands* Part I* Geological Description. NASA translation TT F-ll, 529. von Huene, R., 1972, Structure of the continental margin and tectonlsm at the eastern Aleutian Trenchi Geol. Soc. America Bull.* v. 83* p. 3613-3626. von Huene* R. and Shor, G. G., Jr., 1969, The structure and tectonic history of the Eastern Aleutian Trenchi Geol. Soc. America Bull., v. 80* p. 1889-1902. Wegener* A., 1929, Die Entstehung der Kontinente und Ozeane, 4th rev. ed., Friedr. Vleweg* und Sohn, Braunschweig. (The origin of continents and ocean (1st ed.)i published In 1915.) Translation (4th ed.)i Dover Publications, New York, 1966. Wesson* P. S., 1970* The position against continental drifti Quart. Jour. Royal Astronomical Soc.* v. 11, p. 312-340. Wilcox* R. E.* 1959, Igneous rocks of the Near Islands, Aleutian Islands, Alaskat 20th Xntemat. Geol. Cong.* Mexico City (Trabajos), sec. 11-A, p. 365-378. Wilson, J. T.* 1965a, A new class of faults and their bearing on continental driftt Nature, v. 207* p. 343-347. . 1965b, Evidence from ocean Islands suggesting movement in the earthi Symp. on Cont. Drift. Phil.* Trans. Royal Soc. Lon.* Series A., v. 258, p. 145- 167. Zhegalov, Yu. V., 1964, Komandorsklye Islands (Commander Islands)* Chaps. I-V1I, p. 696-804, in Vlasov* G. M.* ed.■ "Geologiya SSSR, TOM XXXI, Kamchatka, Kurilsklye 1 Komandorsklye ostrova. Chast'I. Geologicheskoye opisanlye." Izadatel'stvo "Nedra*" Moscow. (Geology of the USSR, v. 31* Kamchatka, Kuril and Komandorsklye Islands* Fart I* Geological Description. NASA translation TT F-ll* 529. APPENDICES 205 APPENDIX A Interpretation of Seismic Reflection Data and Detailed Interpretation Notes* for Continuous Seismic Reflection Profiling Records• * Notes are keyed to Greenwich (Zulu) 24- hour clock times* as shown by a four digit number followed by a Z, and Julian dates which appear as a three digit num ber in parentheses* 206 INTERPRETATION OF SEISMIC REFLECTION PROFILING DATA General Considering that seismic reflection profiling is one of the most important tools available to the marine geologist, it Is sur prising to find little written about the techniques of interpreta tion—-the translation of what is essentially acoustic data to data of geological significance, Moore (1969) presented a comprehensive, albeit somewhat brief, discussion of the interpretation of profiling records as a portion of his appendix on the principles and techniques of continuous seismic reflection profiling. Ewing and Ewing (1970) also discussed principles, equipments and techniques briefly. No attempt is made here to treat the subject extensively but a few com ments on the more obvious pitfalls, principles, and rules of thumb are germane. The essence of proper interpretation is the realization that any seiamlc reflection profiling system responds only to the laws of acoustics. The generated sound reflects, refracts, attenuates or is dispersed as a function of the acoustic nature of the boundary on which it impinges or the medium through which it is propagated. Acoustic boundaries are created by the mismatched impedances of ad jacent bodies, the impedance being defined as the product of the bulk density of the material composing the body and the compressions! wave velocity through the body. Structural and compositional characteristics of the sediment or .rock which interrelate with the 208 acoustic characteristics were exhaustively studied and documented by Hamilton (1967, 1970, 1971), and these are one of the basic keys to the identification and tracing of rock layers and structure, Electronic "Artifacts" Because profiling systems are electronic, they can produce a vide variety of instrumental effects and electronic "artifacts" on the records which must be recognized, identified and subtracted from the overall picture lest they be confused with true responses to geological relations, Some of these are easily identified and ignored, and others create considerable difficulty, In this cate gory are signals that result from the ship's 60 cycle alternating current electric power system and other electrical noises such as those resulting from transmissions from single side band long range radio telephones, Many other "glitches" occur, sometimes removable, sometimes not, Another phenomenon easily recognized is the "filter-ringing," "bubble-pulse," or "secondary" effect, On the seismic record this appears as a number of lines of varying thickness and exactly parallel to each other, They are generated because the outgoing seismic ping, or shot, is not a clean pulse but contains at least two sharp pulses about 2b ml111-seconds apart, The top of the top line represents the surface of the sea-floor generated by the first pulse and the entire pattern is essentially repeated by the reflection events generated by the "secondary" pulse, It is sometimes tempting to interpret these parallel lines as subbottom reflectors close to 209 the surface, but this cannot be done unless it can be firmly estab lished that the lines are NOT parallel, The effect is complicated additionally by the filtering arrangement. Unwanted Signals In a second category are unwanted, real reflections from the sea-floor or the subbottom which confuse geological interpretation, Most of these effects are comuon in principel to echo sounder record ing and have been discussed by Krause (1962), particularly the hyper bolic echoes that result from point source reflectors either directly under the ship or off to one side, but under the cone of transmitted sound energy, One of the commonest trouble-makers (but most easily dealt with) is the multiple bottom reflection, Here the sound is reflected off the bottom, returned to the surface, re-reflected off the air- water interface (or the bottom of the ship) and re-reflected off the bottom, The first return is recorded, as is the re-reflected echo, Since the travel time Is exactly twice that of the first echo, the recorder will show a trace exactly twice the depth of the bottom, Depths are double and so are slopes, Sometimes, under appropriate conditions, as many as nine or ten multiples occur, The difficulty incurred is that the multiples, which are usually strong returns, may either mask true subbottom reflections or make them hard to see, Multiples are easily checked with a pair of dividers, On occasion the reflective characteristics of the bottom which permit multiples exist only over a short time span, Here again, any echo exactly 210 double the depth of the bottom Is suspect* The same phenomena and recognition criteria occur with strong subbottom echoes* Somewhat, but not entirely, akin to the multiple bottom echo Is the Internally reflected echo. In this case, the sound energy penetrates the bottom, Is reflected off a subbottom layer, re reflected off the water-sea floor Interface, reflected a second time off the subbottom layer and then returned to the hydrophones. Total travel time can be arrived at graphically with dividers. In both these cases the multiple or the internally reflected echo will have a shape which can be associated with the shape of the surface which provides the initially reflected echo. The easiest test to distinguish between true subbottom re turns and those which appear to be at the same depth is one of the symmetry and travel time. If the suspect subbottom return Is NOT at a position on the record which is 2X, 3X, AX, etc., the travel time to the sea-floor or positively identified subbottom, and If it has a shape different In any small, but recognizable, detail (allowing for vertical exaggeration caused by the Increased travel time), then It Is most likely a valid return* Hyperbolic Echos Reflections from a point source always show on the record as hyperbolae with the apex occurring when the point Is closest to the ship. They can be either on the bottom or In the subbottom, and will sometimes obscure the true junction of two different slopes, for example* Thus the edge of a flat trench floor may appear to extend 211 under the edjecent slope, when whet is seen Is the superimpositlon of a hyperbolic return from a point source on the slope ahead of or behind the ship on a direct echo from a point perpendicularly below it. On occasion hyperbolic echos received from some point-source on the sea-floor off to the side of the ship (but within the sound cone) have a travel time significantly large enough so that they appear on the record well below the sea-floor. These can be confused with true subbottom polnt-source reflectors. According to M, S. Marlow (1972, personal communication) hyperbolae resulting from echos emanating on the sea-floor (i.e., the sound energy has traveled only through water) have a form distinctly different from those which originate from true point source subbottom reflectors— the difference resulting from the velocity contrast of a total water path versus a combined water-rock path. To identify these, computer-plotted families of hyperbolae, calculated for the water path only, over a representative size range, and at the same scale and vertical exag geration used for the seismic records, were printed on transparent mylar. Super-imposition of the proper sized hyperbola on the seismic record permitted a quick comparison and judgment as to whether or not subbottom was being examined. Interpretation Criteria After account is taken for the acoustical and electrical parameters noted above, what remains must still be given subjective treatment, for interpretation cannot be completely rigorous. Patterns 212 which are familiar to the geologist are quite easily recognised, al though the llthology must be Inferred except in those cases where rock crops out and can be sampled by dredging or coring, or better still, by drilling. Where structures, contacts, or beds can be traced or associated with land structures and rock types, a basis is provided for making judgments, or best guesses, the quality of these is sometimes a function of proximity. Such basic features as angular unconformities, faults, folds, drag effects, and deltalc- type bedding, appear in a seismic record much as they would be ex pected in a structural cross-section. Measuring the thickness of strata, however, requires that the tops and bottoms of specific beds be Identified and that the velocity of the material be known. In such cases, certain criteria can be applied for the recognition of some types of sediments (e.g., deep-sea pelaglcs or turbidltes) for which approximate velocities are known and these can be applied. The best situation, of course, is to be able to compare a seismic section with the log of a drill hole, and this was done on Line 43 where JOIDES hole 192 is essentially on the seismic line. Patterns of sediment sequences repeat themselves, and where these are found, they provide the basis for correlation. Briefly, nthe geologist must search for familiar geologic forms . . . (and utilize) a certain amount of intuitive geologic reasoning." (Moore, 1969,- p. Ill), Measurement of Layering and Layer Thickness B«dding closeness, under some conditions, is an artifact of the band pass frequency. Thus, if the center frequency of the pro-' 213 cessed seismic signal is 100 Hs, then 100 H* Is the dominant fre quency that will be recorded on the seismic profile, A 100 Hz signal will print "bedding” lines twice as far apart as one passing through a band pass set for a center frequency of 200 Hz, A statement about the closeness of reflectors that is less than the critical pulse length generally is simply a notation that the rock unit is internal ly acoustically reflective at the listening frequency. When mention is made of "closely spaced reflectors” the inference is only that the closeness is that which the resolving power (i.e., the pulse length) of the seismic profiling system permits. In some "sparker” systems this limit of resolution may be an optimum of A m (Moore, 1969); in this report the resolution is approximately 10 to 15 m. Absolutely accurate measurement of layer thickness is pos sible only with deep-sea drilling. Close approximations, however, can be made using wide angle reflection techniques already briefly mentioned. This technique, together with geometries and appropriate mathematics is detailed by Moore (1969, p. 1070), In essence the procedure involves the ship putting the sound energy into the water and the echos being received by a relatively stationary hydrophone (expendable reditusono-buoy) with the signals being telemetered to the fllter-amplifier receiving system as the ship steams away from the sonobuoy. The progressively increasing obliquity of the sound path through the water and the subbottom, combined with the know ledge of the increasing range through the direct water path and water velocity permits a geometrical net to be established which can be resolved to give the average velocity of the layer identified. If 214 the first leyer so measured has the sea-floor as Its surface, velocity of the surflclal sediment can safely be assumed to be that of the adjacent sea water (or close to It). The average velocity of the layer (or Interval velocity) is assumed to be the Instantaneous velocity of the geometric center of the layer. Thus, two points are established which give a linear gradient. Total travel time through the layer is taken from the seismic record which can be measured graphically to the nearest hundredth of a second. Care must be taken to distinguish between two-way travel (or reflection) time, which Is the time for the sound to make its total round trip, and the one-way travel time which is more quickly converted to true thicknesses and is more accurate In a descriptive sense. All travel times used (herein) are one-way travel times, and directly convertible to distanas if the velocity is known. Detailed notes on the determination of Interval velocities and velocity gradients using sonobuoys are given in Appendix fi. Identification of Rock or Sediment Types The rocks and sediments which comprise the bulk of the geological formations Identified in the seismic profiling sections are divisable into four broad categories, not on a rigorous 11th- ologic basis, but rather on criteria useful in Identifying them from the seismic records. In some cases, refinements in identification result either from association with nearby terrestrial geology or from deep-sea drilling data. The categories are as followsi Turbid1tea, trench, or channel deposits! This type of de- 215 posit Is easily recognized by the parallelism of a large number of closely spaced reflectors. One particularly important characteristic noted by Moore (1969, p, 58) is that "reflections from strata of turbidity-current deposits will mark contemporary low ground" and that "they will be controlled by topography to the extent that truncation of strata will be apparent against pre-existing topo graphic highs of even gentle slopes." The sediment is deposited, as the name implies, by gravity- driven, sediment-laden, turbidity currents. Hamilton (1967) dis cussed the recognition of deep-sea turbidlte deposits exhaustively and presented examples of the various relations one might expect with pre-existing topography, in channels, and in submarine natural levees. Turbidltes seen in the records are primarily deposited in the Aleutian Trench, and are lacking in the Kamchatka Trench. Some chan nels, or perched basins on the Aleutian Ridge, have the same type of deposit. The deposits are not always absolutely horizontal, either In the trench or in the ridge basins. Tilting of these deposits is easily recognized and is, in many cases, a significant clue to local geological processes such as differential compaction, slumping of the down^alope topography containing the deposits, or local tecton^ ism, as in the case of the trench deposits. In certain areas, channel deposits, either on the surface or buried under pelagic sediments, are present in the deep sea. Pelagic sedimentsi This type of sediment is characterized by Its tendency to cover the pre-existing topography in a uniformly thick layer that parallels the topography. Pelagic sediments, which 216 are characteristic of the deep sea, and hemlpelaglc sediments which are defined as being nearer shore and having more terrestrial mineral constituents, are typified by particle by particle deposition verti cally through the water column. Both Moore (1969) and Hamilton (1967) underline the basic characteristic of pelaglcs, i.e., that they "drape1 1 over the topographic highs upon which they are deposited. Complications ensue, to a certain extent, in applying these criteria, for winnowing (thinning) of the deposits can occur over topographic highs where weak currents either remove the sediment once deposited or cause differential deposition. In addition, pelaglcs deposited on a flat surface are also flat, and may be confused if care if not taken with turbidites. In thick sections this Is not too much of a problem because the pelaglcs lack the strongly developed layering (i.e., internal reflectivity) typical of turbidites. Pelaglcs, especially after they are lithlfied and consolidated, may be faulted or intruded like any other rocks, and thus achieve the characteristic "truncation" which is characteristic of turbidites. Basement rocksi The term "basement," in common usage, is fairly flexible in its connotation. According to Howell (1957) it is "an underlying complex that behaves as a unit mass and does not deform by folding." Another definition from Howell (1957) Is a "complex, generally of igneous and metamorphlc rocks overlain un- conformably by sedimentary strata." In the interpretation of seismic profiles the term is commonly modified to "acoustic basement" unless the actual composition of the rock is known or can be safely Inferred. In this context the top of the acoustic basement is the last con- 217 tlnuous coherent reflector below which there is a significant volume of rock within which definitive structure cannot be Identified. Another term used in describing acoustic basement is "opaque," with the Inference that the rock mass Is opaque to sound energy, thus precluding reflections from within the mass. Conversely, some rock masses are termed "transparent" because they easily transmit the sound energy and reflect strongly off boundaries below. Both of these terms, although highly descriptive, are not in good repute be cause they are optical rather than acoustic. Acoustic basement is recognized in all the sections described In this dissertation. In those sections which include the Aleutian Ridge, Its Identification is closely estimated by association with known shore geology. The same applies for those sections approaching Kamchatka. In the open ocean, the composition Is only inferred except in the vicinity of JOIDES hole 192 on Line 43, where there is sample Information show ing that the basement is basalt. Layered, structured, and miscellaneous type rocket This in cludes all rocks not included in the three categories mentioned pre viously, namelyi 1. Volcanic, pyroclastic, and associated llthifled detrital, volcanlclastlc and pelagic sedimentary rocks (principally along the Aleutian Ridge) which can be extended from known island exposures out to sea, and identified with reasonable confidence. 2. Semi-consolidated layered deposits which fill large basins off the Kamchatka Peninsula and along the Aleutian Ridge. These should not be confused with the turbidite-type deposits in 218 small basins which are an order of magnitude smaller. 3. Slump deposits, which notably lack internal structure, but which can be Identified by topographic characteristics. APPENDIX B Notes on the Determination of Interval Velocities and Velocity Gradients in Sub bottom Layers Utilizing Radio Sonobuoy Measurements. 220 A. DEFINITIONS Terms which are used In the equations and relations discussed In this appendix are defined as follows: Vq ■ velocity of the compressional wave In the surflclal sediment at the sea-floor. Vp - instantaneous velocity of the compressional wave any where In the layered section being studied (in meters per second). V - (Vee-bar) average, mean, or Interval velocity, a * velocity gradient (In meters per second per meter), t - one way travel time (In seconds); also can be used to identify depth in the section or the thickness of a layer. h - thickness of an Interval or layer (In meters); also can be used to indicate depth In the section, e - the base of natural logarithms (2.7182818). B. REGRESSION EQUATIONS Utilizing techniques developed by Houtz and others (1970, p. 5093-5511), the following can be determined* a. For lny^iflfratieoua velocity (Vp) at time (t) in the section use polynomial in the form (Houtz and others, 1970, Table II): V - A + Bt + Ct2 P where (in addition to definitions of V and t above) P 221 A “ surface velocity (Vq) in meters/second g ^ “ coefficients of regression unique to sonobuoy solution In any one particular locale or environment, Examplet for the Aleutian Trench (Houtz and others, 1970, Table II), V (krn/sec) - 1.520 + 2.641t - 0.955t2 P b. For the average or mean velocity (V) of an interval (some times called interval velocity), use the following equation: V - A +f + f 2 This equation (Houtz and others, 1970, p. 5109) is derived by integration of the instantaneous velocity equation using the technique of Houtz and others (1968; Appendix 2). Example for the Aleutian Trench (Houtz and others, 1970, Table II): V (tan/sec) - 1.520 + 1.321t - 0.318t2 C. EQUATION FOR INTERVAL THICKNESS WITH A LINEAR VELOCITY GRAMENT Sound velocity curves are customarily exponential (curve- linear) in form but their upper portions may approach linearity sufficiently to permit the assumption of a linear gradient in the calculation of thickness for shallow layers. The utility and accuracy of measurements using linear gradients will, of course, be dependent on the sound velocity conditions at any particular locality and the depth at which the velocity curve starts to 222 become strongly curvelInear. The equation for thickness, assuming a linear gradient, is given by Houtz and Ewing (1963) from studies of layers by ex plosive seismology. The application of the same equation in con nection with sonobuoy measurement techniques is discussed at length by Hamilton (1967, p. 4211). In both cases the equation is: V (eat - 1) h - -2-------- a D. PROCEDURAL STEPS FOR DETERMINING VELOCITIES FROM SONOBUOY DATA USING REGRESSION EQUATIONS 1. Assemble the data from the sonobuoy wide angle reflection solutions. These solutions provide (dependent variable) as a function of t (independent variable). Any instantaneous velocity (vp) at time t Is also approxi mately an Interval (or average) velocity for an Interval de fined by the sea-floor as an upper limit and time 2t as a lower limit. 2. Compute a regression equation in the form: y ■ A + Bt + Ct2 which is a rearrangement of the standard blnonial form: y - Ax2 + Bx + C Use the x, y (V^, t) points from the sonobuoy solutions. Determine V (surficial sediment velocity) from: o 223 a. Assuming environmental conditions approaching those listed by Houtz and others (1970) and utilizing their "A" values in Table 2. b. Assuming (or knowing) surflclal sediment types and utilizing values given by Hamilton (1971), Tables A^l or A-2. c. Determining sound-velocity in bottom water from near est known hydrographic data and applying ratio of velocity in sediment! velocity in sea water as deter mined by Hamilton (1971, Appendices A and B) (1967, Appendix). Methods in b, and c. are much more precise and are to be preferred over a. With A as Vq, the two coefficients B and C are developed as a first approximation. This la the purpose of computing the equation. 3. Plot the data points from step 1. Plot the curve obtained from the regression equation to see how the data fit. 4- Force the curve through the one point where the deta Is most accurate by repeating the Vq point ten or twenty times as individual data points. Actually this forcing is done in step 2. Using the C coefficient determined in step 2t and the same xt y (Vp* O points from step lf correct the velocities (call them Vp's or v'8 88 you will) with the following equatloni Ct2 v _ u _ p(t) p(sb) 12 where Vp(t) * the true corrected velocity Vp(sb) " v*loclty from the sonobuoy solution t ■ one-way travel time from the sea- floor to the depth of the V P 22$ C - regression coefficient determined In step 2. This correction is derived in Houtz and Le Pichon (1968, Appendix 2, p. 2660). 5. Repeat step 3 using the corrected velocities. RESULTi The Final Form Instantaneous Velocity Curve. This will plot slightly differently from the curve in step 3. 6. An approximate mean (interval, average) velocity curve which Pi ots t (one-way travel time) against V (interval velocity for the layer between depth, t, and the sea-floor) can be constructed by considering the interval velocity at depth t on the interval velocity curve to be the same as the cor rected instantaneous velocity (from steps 6 and 5) at depth t/2. 7. However, a preferred and more accurate way of doing this, which takes into account the curvellnear nature of the V P plot, is to derive the mean velocity (V) curve using the cor rected Vp velocity data points from step 4. Use the follow ing form from Houtz and others (1970, p. 5104) and Houtz and Le Pichon (1968, Appendix 2, p. 2639)t “ v - A + ^ v 2 + 3 where A ■ surface velocity (V ) o 2 2 6 g c “ coefficients determined In step 2 t * depth (one-way travel time) — - interval velocity (from time t to the sea-floor. 6. Thickness determination! a. To determine the thickness of any layer defined by depth t and the sea-floor, use formulai h » Vt where h “ thickness V * interval velocity from curve (step 7) t - depth (one-way travel time) b. To determine thickness of a subbottom layer (layer #2 in sketch below) defined by depth t, and depth t^, use the following formula: h2 " V2f c 2 " Vltl S * a , F t As, £<xymr fx — — ' t^ ----1 ' V e l o c i ty ad ~ t ± i----------------------- W t o c i f y ad APPENDIX C Dredge Haul Data 227 226 Haul Number: Coordinates: Location: Depth: Misc.: Megascopic: (Shipboard notes) Microscopic: Age: Haul Number: Coordinates: Location: Depth: Misc.: Megascopic: (Shipboard notes) DREDGE HAUL DATA B-29-D-1 Lat. 52#37.1* N Long. 174°51.1' E North slope Aleutian Rldget 80 km west of Buldir Island. (Close to start of Line B-30.) 750 m - 400 m. Numerous bites with pull up to 10 tons; good re trieval; about 500 lbs of rocks. Parte aray. medium crystalline hvoabvssal rocks; phenocrysts of auglte or hornblende, sometimes in clusters; fresh breaks indicate bedrock. Exotics - rounded pebbles, hard black basalt, vesicular basalt, chert. Hornblende dacite. Good feldspars and hornblende for dating; shallow hypabyssal intrusion or surface flow; good calc-alkaline rock. K-Ar date for hornblende - 1.4 m.y. (early Pleisto cene). B—30-D-l Ut. 52°09.5' N Long. 172°57.1* E South slope Aleutian Ridge, southwest of Agattu Is. 3400 m - 1900 m. Strong bites at 1900 m (20-25,000 lbs. pull); dredge snagged and lost. Small mud sample from depth recorder. Fine, green, sticky, silty mud with a few rounded, black pebbles, probably basalt. 229 Haul Number: Coordinatest Location: Depth: Misc.: Haul Number: Coordinates: Location: Depth: Misc.: Megascopic: (Shipboard notes) Microscopic: Age: Haul Number: Coordinates: Location: B-45-1-D Let. 53*39.9* N Long. 160°41.7* E Off Cape Shipunskl, Kamchatka. 1500 m - 1000 m After several good bites, dredge locked on and could not be retrieved. Lost dredge and 106 a of wire. Bottom probably hard Mesozoic or early Tertiary bedrock. B-47-1-D Lat. 54°35.5* N Long. 162*28.7* E Off Cape Kronotsky, Kamchatka. 1800 m - 1500 m. Disappointing retrieval; almost a complete blank. Two ice-rafted (7) pebbles of crystalline rock, one well rounded; two pebbles of semi-consolidated sedi mentary rock (greenish silty sandstone) probably from outcrop and dredge rounded; green mud. Calcareous crvstal-vltric tuffaceous siltstone (arenaceous tuffaceous limestone); 607. of matrix fine crystalline calcite; some forams and occasional diatoms; quartz and chert fragments. CALCAREOUS TUFF Pliocene - Pleistocene (based on diatoms) B-49-1-D Lat. 55*40.0* N Long. 165*13.9* E Aleutian Ridge, northwest of Baring Island in the Komandorskiyes. Depth: 1800 - 1400 m Haul Number: Coordinates: Location: Depth: Misc.i Megascopic: (Shipboard notes) Haul Number: Coordinates: Location: Depth: Misc.: Megascopic: (Shipboard notes) Microscopic: Age: 230 B-38-D-1 Lat. 54<>00.7' N Long. 167°29.3* E South slope Aleutian Ridge south of Medni Island; outer rim Aleutian Terrace. 3200 m. Some bites, but little pull; minor retrieval. Dark green terrigenous mud: some exotics which ap- to be rounded beach pebbles; no outcrop material. B-3S-D-2 Lat. 5A°06.7* N Long. 167°25.3' E South slope Aleutian Ridge south of Medni Island; outer rim Aleutian Terrace. 4000 m - 3500 m. Weak bites; retrieved about 200 lbs of soft semi- consolidated sediment, a little mud and a few exotics. Bulk of haul gravlsh-green. slltv. fine-grained sand- stone; no visible foraminlfera, some layering and streak banding; small lense of pea-sised granules. Probably from outcrop down slope from rim of Aleutian Terrace. Exotics - Angular to sub-angular pebbles and cobbles; well lithlfied sandstone, black igneous (volcanic) pebbles with fine-grained ground mass and no pheno- crysts; conglomerate. DIATOMITE - diatoms and sponge spicules. Plio - Pleistocene (Late Marine Series) (baaed on diatoms) Misc.: Megascopic: (Shipboard notes) Microscopic: Age: Haul Numbert Coordinates: Location: Depth: Misc.: 2 3 1 Haul B-49-1-D (continued) Many strong bites at deepest part of haul (1800 a). Retrieved dredge full of rocks. Dark volcanic rocks; fine-grained porphyrltlc vesicular basalt; very hard; elongated vesicles; some pieces of well llthified conglomerate. Shales and siliceous shales - Tan colored; very fine grained; indistinct bedding; soft; possibly diaton^ aceous (?); some shale full of chert stringers with conchoidal fracture. Cherts and chertv shales - Rocks resemble the Monterey formation; several large pieces of chert; shale frag ments fractured and brecciated; slickensides (?) noted on one large rock. Exotics - Hornblende basalts (?) - patch of copper (?); laminated siliceous shale; greenish grano- diorite; fine-grained vesicular basalt with olivene. Highly vesicular, flot^banded porphyrltlc auelte andesite. Calcareous diatomite. thoroughly llthified. Basalt - K-Ar age - 4.6-1.0 m.y, ■ early Pliocene. Diatomite - middle-late Miocene. B-56-1-D Lat. 53*30.7' N Long. 169*58.9* E South slope Aleutian Ridge near Komandorskiye Is lands, but above Aleutian Terrace (close to turn from Lines 35 to 36). 1700 m - 1800 m. Retrieved a dredge full of sub-angular rocks of two basic types: (1) soft, punky, dlatomaceoua shale with evidence of mollusc borings, and (2) hard slate, argillite, chert and volcanics (7). 232 Megascopic: (Shipboard notes) Microscopict Age: Haul B-56-1-D (continued) Hard llthified rocks a. Volcanic rocks, fine-grained. b. Strongly llthified shale or argillite. Soft sedimentary rocks a. Tuffaceous sandstone, round, but with a manganese crust (not dredge rounding) b. Punkv. diatomaceous shale, with worm burrows. a. Volcanic wackes, some altered. b. Albltized metavolcanic tuff breccia (with high pressure minerals pumpellylte and laumontite). c. Argillite. d. Lithic volcanic wacke. e. Microcrystalline £hert. f. Diatomite. a. Diatomite ■ Pliocene (from diatoms). b. Tuffs, wackes, argillites and cherts ■ Early Marine Series (pre-late Miocene). 165* 60’ t f 5*' u w v fn fiT T 0 * M u r o m * * , i m MC«0 M O U t NM M . OCCMOOUMMC O fU C I N O T E Detailed descriptive notes concerning the field analy sis, methods, operational problems and general interpreta tion are available in the dissertation copy filed in the Department of Geological Sciences, University of Southern California, in the files of the Sediment Laboratory of that department and in the author's possession. Interested read ers are invited to examine these detailed notes in those locations. Following publication of the major portions of the research, these notes will also be filed with the National Auxiliary Publications Service, c/o COM Informa tion Corporation, 909 Third Avenue, New York, New York 10022. Access to those archives can be found by the author's name and the dissertation title. 233 •IK A/I *«*M Tf COI (V M 3 , V I * * WTIUN09 • » ^ ► *»*<» o tiw m • < * n m * A Q T to AllMlMMn | V 7 I H V F ¥ 3 f i . 0 4 1 S9I .091 170* 175* W k C I rmrr*t4m m M C M fA" ,y * ) ZHS-tlijf i .ff'm rft - r JWr *Wln >**<■« <* W W M f ll MDI i . 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I I 3o i «XD-ir» m * ™ tool 9(27 th JO* 227 V e r t i c a l * Z U a g y m r a d j x m . - 1.05 x s p e t d . i r v t j u o t i k«. mum d c h m *— * « ■ > WMry o* 1 m m n * u**a« ae- t*oo ■ s X to X ts X 20 IE 25 N a z oUcaJL M i t es a t 90Kruorbs AO /3 2D 2* 90 33 4 Hit B 38 -50 n « SO F . n . — \ TTTy -TT7 — . r . . J - 1-^1— I X z lo 7 n o i*rs a t 9 .0 K n o ts W hi* . pwm £t«0 — O-- i>*e. A 50 ISoo 1-0 -2 2 5 b KA7UZ?) 18002 l - j o o z . irif» 3H7-m J O - 217 & *o n . “ 1.05 x spid. in* k . n o ' 6 . s J.& 137 F i h e t * % / i o i t * . 4*fc .f^re (y»)— 8o w ZJ7BT Vv e 9-0 le% 3 0 0 0 -575o tysoo $ - 5 2 5 0 — 4ooo 675o — 2-0 3.0 40 IH /O /3 20 2£ -JO i i ~:~"r | i J fiL e s a t 9 .0 K n o ts ___ / J 2 0 J O 3 3 -A? 45 &0 i l l i i i — i r 'iT T v e .ta r s a t 9 0 K nots -75oo 0 2 5 0 J o o o - 5 - 0 6o LINES B 4a ilZ«ii£ian, 2?*«ne\, -41- 40 39 T k r t a f a - C a t pabtftu «k M i M i l l Y 39 SU JO Gtrrmhd* Mm paUatc* wU ^1«>mi »» ri4> < n f c i « / M iu A on J * A . 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ScfrAL, p m rsons.1 w i v — ' - SMS rr^r idfa MAincud on' ^ r ^ i c a Z r j t n y i W t o n ■ i . £ J 5 J< spssd zn iC r t o i s Acoustic Aeucmout M-lj I4WMMM 338 / S 2 0 zs I X I NaLuUcaL J f lie s a t 9 .0 Knots A O rs 20 A O A S so AS SO r ...|....|....l....|....|....|....|....F-71 KcZomeisrs a t 9 .0 Knots WMS* TTM£ perm oeconos C l WTWKj 0** ujA' ^ TRA,s/e.t_ O-------o ---— 750 I5oo- 12So 3ooo 375o I o lid* Jbup HCDt i» o * iacoi 9&x>m _ 543071 jW7*t 54cO nv i2£Oi ttaot aafTw _ 9-5*4* ■ + * • & . su^ IIO O X 1030 a 9 9 D m . _ _ _ 5 | O tti ' M o H t 2S7*T <£— Ebo bue XD.XJ9 45oo— 3 0— 1 5250 6 0 0 0— 4 o — 6 7 5 o 7500 — 5-o 6 1 5 0 ---------- — --------- M 3 w M H k oerrw* utuHt vmvoocrf of soomo « * j u*n«A of- * » w / * 9 0 0 0— 6 o I I 3 D 2 II0 0 2 1030 Z 5 l 5 > © T n . _ 51 3D in 25TT &• loooZ S D C m . J3>.2» 09302 186™ 95t*» csmdx. ceao* c6ooz 4W»- y)W»"- 4 4 — */►>* zart 07i> 2- 0*002- 0630* 33»7m. 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LINE B 46 JVcLuti oaL jf ila s a t 9 .0 knots 3e> AS 4o JCiZo7*tatm rj a £ 9 .0 knots 'V‘ 7 LINE B 46 TtMe WATBt C j> c p ih oum w*n TWKml Q 4 e m ) 1*0 V e rtic a l Exaggeration - -15oo 2 0---- ILOr £ rD2S2. cut Ui>c B-47 3o- 4 0 - ia O O O 1 4 c ol 1631 £ *©©>«• 4U5m t b OtT JP2U LINE ticaL Ewffiraiwji =1.05 x spied, ut knots o L fO m / j n NautvcaL M i AO r-..[■. .. | K i l o m e t e r s a 4SX>*» SOlii (531 i UtCjr 1 3*0 £ IlcOl 47I8»- _ _ _ 5p33w. SMDm of lo^ r gbkJ lam] ut.tam* i f c o e J i Hioi m» £ 5835 m 5108m JO'iU. WofeL €oiifc I I O O Z 58i?m 1 0 - 0 fcH’ k s LINE B42 Trench* Q £ /O /S 2 0 2 J S 3 0 l_ : . _zi_~ ■ : i ~ _ i n _.~ . . i ffaidtucaL Miles at 90 Knots 0 - 3 / 0 /4~ J O IS J D 35 4(9 4B 40 I 1 1 1 I I | -• | | | — | JCzZomebsrs at 9 OJCnats i i o o i *>*>£ iooo ir ogaoi &k>\l 502?m._ SitOrr __ SoSST"" _ 4-72Sr« 0 -0 k H 0 6 C fT fy fe ttc . " C D k L J TD.Z32-’ 4-6 Wm h aa»t» JCajyichatJba. Treruzhs L~_r_ i o+x>i C 9 < > \ 1 GDVJ ' T - 0 . Z 3 2 - 6 STMT JTW Foe oiaoi <fW2 to tJ JD 2 5 2 . Tfc^o*^ | . t » e *4T atsfr 9 2 > t t» flBooi *«6" imm 9 .o f£* i •J.B W M e t D»T H A W H e t WAci-ry c» acuw* u i m u — 10C O - m / M c . w*roe, (Mer«a> omr- « mn tuml O 15b 1500 (o 0 2k>JE J I t o f F c f e X.M»£C»0 J D Z iZ . ewhc irnm 9©fcK U&> 3ooo 2 0 37 So 45oo 30 5iSo W t 6TACTUMC B-47 JV2M — £ 0 0 0 4o » ■ £ > t # h . ©OH KyMt- L i t J C n? oe^r 9©m *750 -75 bo 5o 6 2 .5 0 ISOO THy/<*»e. ^ 0 0 0 -60 V e rtic a l* E xa g g e ra tio n , - 1 0 5 x speed, zn k n o ts p m / utbb, *n mawu^n; , Jifnil. ieri^«r 1 (but -Zh£t vuUads. It ofhfy \speed zn knots o I 1 to tS 20 23 I I I I N a u tic a l M ile s a£ 9 0 Knots /O /*- Jto S O □ i ! • • • i | - - - | • | — r~ | . I - . - r i JCHameiera o i SO Janata A (Srohtn. normal. /*nI d a x * » c L u n * n .{ i £k* t r e n c h . < / No iulhtitm rmfUcion nMtafMiii 04 t Mwtl J lw y j4cdii<^ k Jh w w 6 m <rimaW*iy<fr» Jb6* yiiwnli* t ug h tj f S p i c u ta d * * * K am chatka. Trench LINE /o /5 2o 25 SO I I I I N a u tic a l M ile s a t 9 0 K nots JO /*• So L1ZL~-TL i I - I I r z r n \JCtlame6ers a t QOJCnots j i e a t L t O c ■ ut / ■slump No t i p i i / i c a n t j iJ M < » i h rmfUctem — pStigtr 6 m> ZNuipxnm Otitmmm (dvtemli, tuffactmn j f^K r a r aw* »* ayJ t f c i Z meaok LINE B 4Z ■ Z V » ; T«ME WA.W* secouos oePtH {nenab) 025--375 0-5— 150 0 75 -I12S Z M t 2 tatt ms*« IMA* I2P-W gioUf. T Hie I • O 15oo — X I V e r tic a l E x a g g e ra tio n --1 0 5 x speed in . WM* •••TV* •«>1 !•• Mk«*TT M WMU* €)• IVOO LINE B-48 WMee ocptw (Ht-nes) — O 3T5 1125 ZllH UPw igoo 2 J *9 t cm*** CfUrtS 6^11 ZW3A 2.MC. fitHf Z « c f ir # 0OCJ /£ ? 5 X .$pe«i in . knots Mumo *m ujmu, cm ncomyMc. B48 WMQB oepw C hctbsJ T5o I5oo a/' H H W 1 puhut Mvr M w a C M t U X I W <W IMMt, 3150 — 52.50 o L 5 X 1 0 f S I I Jlau ticaL M iU s to is JO 28 I_: i_. I. 1 Kilometers at 9 . 20»1 tfJol )9«0 f t +4 50m__5Mm. WMK DEPTH ^McnesJ WM net ( hci 15o I5oo /a □C (5 I 20 ~ T ~ I D J^auiijcaL Tables at 90 Knots /o ts 20 2S JO JS ~ i ~ i ~ — i i i ~ t KilomjcJtvrs o£ 90 knots 1* l» 0 O 2 r 4090 m nap* 4z4om ITOOZ: #TZ,tb (5c naoa i4c«a: ~ 9 .0 ck ““ ’i 20002: B*>* BOO f t 4450m. 51*( n flUhn T t & o H t . e o tX JDJSa. 57i5m tM6l IDZSi A l e u t i a n * TreixcJi, /O /S 2 0 -23 J O -i— - i • ri — ~ i W M B R T In\C - D C P TH (-S ttO H D i) (mcicrs) <*** *** T* - O — -0 TfauhijcaL J*files a t 9 0 kjuyts — -150 /£> *5 J O J S 3 0 J S 40 4 6 J O I ' i i i i i i ~ i r — i KiLoTtteixTs ah 90kju>ts 6o o— | o I*)3o* »00 » *lft< rv __ SMftm 0Otr JD2U H S O jr iUOrm oaf t VO62 i»oo* < 0 * 0 w t <jfe.O tfT 5*5 »w c D *CT ' 6000 twez. 1CZJJ. 20 3 0 4-o JlZeu.tuiru TrerucK, Tbmar&Zjr wnwWacJ cwiftounte »f A« JW/bttu . Xy«i• AfuwAiaw. V k r i i c a L £ x a 0 ? * r a £ z o n . - /#5 x y r f **• LINE B 48 (t) fOOOfaavaa. artamaly li HU £ S' o c 5 X to hi /s H I o c s X M aubioaZ JfiU t o m m o m m 3 « ru i^ Z f£ u rf (XtrmAJui*r*/C*yat) 1 . 0 5 X . S p m a d v t , f o % a t s \ - r a f f m r i i t m im iftjc AfcaAM ' v I V 7Am crtiiiiy ntrM, */ Me. ^ n m t i a L r t uAm ite AruAiir inj t^uiw iun*ii jpuwdfr 4*4 C*naliy 4iW Oadny(7fX>)^iff B48 O 5 t o / S t o M S S O - I ■ — . - I-: • ■ • I _ ; • • ■ I - • : - 1 • J Jfazdkicul E lite s a t 9.0 to o ts o s f o m s o a s s o j s + o i & s * LJT-: l 1 • u_- j • - -jJ T77" - • I * • • • I 1; • ■ : ' l - v H Rilorrueters a t 9.0 to o ts at' -W, J«W, ? i * 9 * i y -r*/lmcd±m '-fhmu-f-f- rfi^ r If rw » nc/2«6*s a/ jifiu/iMNM. monMiomumuJt JQ ta e S M fca J U m * 1 3 1 fc W S s J k e tL , p e r * I u iiltw .) Y TXw criuia^ w t n e r t J L */ Jttmdnr*. udtar* i A * liiruAuo o U ryu-W eknr«i6 m rm m d f y m m i .r m i t, a n d f a n t i C ~ ~ tly a n d ( * * > ) * $ JT . 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MEASURED & REGIONAL (GAMMAS) 48000.0 48400.0 48800.0 49200.0 49600.0 50000.0 B f l R T l E T T - 1 9 ? 0 - L I N E 3 0 o CU o LD oj o (J cr o >: • y; 01 cr o o r- co oo 0 o. o ID 1 • f + j o« 6 o o o. 22 + +++++++ ooooooooooO© 21 DAY 225 HR 22 MIN 10.00 MEASURED “ + REGIONAL -0 RESIDUAL -LINE 30 00000000000000000000000000000 8 0 1 9 1 8 REGIONflL - 0 RE SIDURL OOOOOJGQOGOOOOQOOQOJ^^QSii^Q®^®?00000000000000 16 J£OQ055®9OOOOOGOOOOOOu OOOOOOOQOOOJGOOOOOOOOO oOOO000000000 000000 0000,00000000000000000000000 * ■ + 4 4'+- + 4 4 - 4 - + 4 4 4 - 4-4-4- - T " " * * * oooooooooooooooooooo T I ] + + + . + + + + + t + + + + + + + + + + t + V o o o 8 o 5 o o o o o 6 5 o o o o o o o o o o o ( ? p o o o o j o o o o o o "T 1 ------ 0 DAY 82b ~T~ 83 o 3 o o 6 q o o o o o o o o o o o o o o o o u o o o o o o o o o < * + + ■ * + + + + +' + 4++++ + + I 4 OOOOOOOO^OOOOOOOOOO^rOJI'JuOOU ® „ o o o o ^ o o o o o o o o o o +++ + / / ♦ \ + + + i t + + * ■ t - T t V . * * " • % . ' V / *s V + - / C D ft ® to C T ' CD - • X 2 XI c o * — ro 01 -o ro -500.0 • -C o c 1 ♦ I o ^ C 4 T C_ -c r & .c o' o c c , 4C T ‘ - » A C . - f C - A O - V c - r """ 4 C >* 4 C f 4 O + O 4 O r O 4--------r * - ^ L - - , Q - . . . . . . . . ----. . . 100.0 300.0 700.0 1100.0 RES IDUAL (GAMMAS) 1500.0 •48000.0 48A00.0 48800.0 49E00.0 49600.0 50000.0 MEASURED L REGIONAL (GAMMAS) MEASURED L REGIONAL (GAMMAS) >48200.0 48400.0 48600.0 48800.0 49000.0 49200.0 49400.0 BARTLETT-1970-LINE 31 000° 0o^ s * o_ o o O ' o to <r o ¥ o s s £ o zj • 2 o CO W Ui 1 or o . o to ] o o o * s r ° ° ° ° o 0 oo DRY 826 HR 6 MIN 0.00 MEASURED -+ REGIONAL - 0 RESIDUAL - 00 + + 0 o 00 000 0 0 0 ° 0°OOo ° 0 o ° 0 0 0 0 0 °00 O q 0 0 o + + * ■ + + + + Oo 0 + + + + + + I % ) RESIDIAL - ♦ \ t t 4 ♦ c c c o o o + c - o o o c c r O 33 -< ro r o 0 3 O 13 1- 4 r r n Kl "4 r o CO 3 u -H X 3) 2 S ■< r o r o a t r o r o ui o V 4 4 4 t t 4 4 4 + 4 4 4 4 4 *4 4 4 N*x > C c . o o o c . o o o o o o o c c o c o C - o o o - 1000.0 -600.0 -£00.0 RESIDURL c c 4 C rr. 4 4r £00.0 (GAMMAS) 600.0 1000.0 o o o + ° 31 + * n :o z: o cr ^ " 2 _o o CD O O O o 83 o ho T O') T O ■o CU ^ cn co (T z: o £ » cr O O o o <T> - ir 5 J o 2 o ® ■o 111 t“5 ( Y- 00 Lt -r Q O U J * oc o Z5 o c o CD X 0 0 L d TL O o ir 00 .T o o CU 00 zt Plate 27 DRY 825 HR 22 MIN 15.00 BARTLETT-1970-LINE 32 MEflSL'RED & REGIONAL <8RHM,^S'» RESIDUAL <GRMMAS> r 500.0 49600 .On 49500.0- 49400 .0 49300.0- 49800.0 300.0 100.0 - “ 100,0 ~3oo;o DRY £86 HR 8 MIN 15.00 " j Pl*t* 28 - + . ' • ' A -500.0 DAY 686 MW 6 KIN 39.09 . -0 RWtOtflL ;-j> . jc' - t - , , Z - . ■ $ t - v i m ;*■* ^ I ^ 3 H z 8 § o 5 5 to ro ro m MEASURED £ REGIONAL <GAMMAS) 49800.0 49300.0 49400.0 49500.0 49600.0 49700.0 49800.0 49900.0 i . * - » — . — — j. i ■ » « R K 3 « J Q * - .7^* 3 z 2* ro r r* o : .f * o o qo ro 8 -tooo.o -boo. o -eoo.o eoo.o eoo.o REStDUfiL <GfiMMRS) 1000.0 9RRTLETT-1970-LINE 33 BRRTLETT-1970-LINE 3 * 4 . CO o - 0 0 0 0 o ()o gj ■ - g E o • _ tfl 11 Plate 30 DRY 886 . DRY 886 HR U * . HR 10 . h HIM 5.00 V . 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REGIONAL (GAMMAS) BARTLETT-1970-LINE 3B O o - o o to o o- 00 CD “ 3- O O ' a> < n 3- O o rT cn *3“ O o - C U 0D rr 0 0 1 o c n T Of O in o o - o cn co a z o * o - o x: 31 <r C D n „ o o o o o ° ° ° ° ° 0 0 ° 0 0 ° ° ° ° ‘ + + + + o O- o PI HR 4 MIN 50,00 MEASURED -+ REGIONAL -0 RESIDUAL - ♦ 0 0 0 0 0 0 oooooooooooooooooo 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 + + + + + T 0 DRY 227 ESIDURL - * G3 33 OOOOQOOOC OOOOOOOOOOOOOOOOOOOOOOOO 5000000000000000 .00000000 oooooooooo.556«».«9»;: + + + + ' r o o » r* o» KJ U> 3 O X 3) Z -< o •- no . co ro o 0) o o o +o < 3 > CM- o + o+ o+ o 9 H D 4 0 + O + o + o +o -Q © o © © HO + o + o + o + o + o + © + o -500.0 -300.0 -100.0 100.0 RESIDUAL (GAMMAS) h— r-e- 300.0 49000,0 49200.0 49400.0 49600.0 49800.0 MEASURED & REGIONAL (GAMMAS) 500.0 50000.0 flRTLETT-1970-LINE 37 I CD C E s z z a: C D a: o ► * — H C D LU Ct O L lJ a: z> C O a : LU TL O o CD O i n o o o I D o o c u o ID o * o o o o ID O O' 00 CO - r o o C D C D o O ' Tr c n ■ 3 - 0 01 cu cn r S ~ + + O o q 0 0 0 ?°°oooooooooSon + + + O00ooooo5fi9 © C D CU DRY 887 HR 16 MIN 55.00 MERSURED -+ REGIONAL -0 RESIDUAL -♦ 7-\ OJ r o ®«9oo0 8 01 _I_ + + + 0 0 0 ° 0 q ° 0 q + + + + + ° 0 0 °00o OOoo 000 °00 OOo OOo + 4 °00 0 0 0 0 0 °00 00*09 • c . no “i ------- 1 ---- & — i - - - *--- 1 ------- 1 ------- 1 ro -10G0.0 -600.0 -200.0 200.0 600.0 1000.0 RESIDURL C GAMMAS> 49200.0 49400.0 49600.0 49800.0 50000.0 50200.0 50400.0 50600.0 MEASURED £ REGIONAL (GAMMAS) DRY 888 HR 14 MIN 0.0 MEASURED S. REGIONAL (GAMMAS) 50000.0 50100.0 50200.0 50300.0 50400.0 50500.0 50600.0 _i_________i _________i _________i _________i _________i _________i RESIDUAL (GAMMAS) -500.0 -300.0 -100.0 100.0 300.0 500.0 BARTLETT-1970-LINE 38 " T “ 13 18 ~ r u “ i“ 10 REG I ONfiL -0 RESIDURL -♦ T 10 "7 9 “T ? 0 DRY £88 DAY 888 ~T" 83 88 61 _ L 03 T3 _X_ 33 0 + 0 0 + MIN 35.00 * P r r » U 00 o 3 ) -< ro ro RESIDUAL (GAMMAS) 50000.0 50100.0 50200.0 50300.0 50400,0 50500.0 50600.0 MEASURED a REGIONAL (GAMMAS) *0 s r U > u > 8 a i m 0 1 + 8 < n M § I o 8 (0 i ♦ 3 O ' * - • I 3> MEASURED a REGIONAL (GAMMAS) 49500,0 49700.0 49900.0 50100.0 50300.0 50500.0 ------- 1 ---------1 ---------1 _________i ________ i RESIDUAL (GAMMAS) Z 30 -C -500.0 -300.0 -100.0 100.0 u * - * r o o o > n o • co CD" ( J 1 “ L 00 ID 7 ) H i m H CD O I 2 m CJ % o LINE 43 E6I0NRL - 0 RESIDUHL - 0 0 0 0 0 0 0 + 0 ~ r 13 T" 11 ~ v ~ 10 o+ + + T 11 1 “ 10 1 9 T 8 o + “T e 83 DRY HR MIN o ro ro -500.0 -300.0 -100.0 100.0 300.0 500.0 o RESIDUAL (GAMMAS) o _________________________________________________ ________ 49500.0 49700.0 49900.0 50100.0 50300.0 50500.0 MEASURED G . REGIONAL (GAMMAS) z a H i i z x -< o ( f i ro 00 o MERSURED & RESIONRL (GRMMRS) 50000.0 50200.0 50400.0 50600.0 50800.0 51000.0 51200.0 51400.0 i . — ^ . i ------------ 1 i_______ i ____________i ____________i ____________t _ RESIDURL <GRMMRS) w s I 1+ X T 1 a -500.0 -300.0 -100.0 100.0 300.0 500.0 00 + o BARTLETT-1970-LINE 44 RES IPURL 0 0 0 + 0 1 5 “T 4 "T 3 o+ o+ 1 --- 0 DRY 830 83 ~r 23 “T 22 “T 21 "T" 20 +♦ ~ r 81 ~ r 80 ~ T ~ 19 18 Plate 36 . -] ro -500.0 -300.0 -100.0 100.0 300.0 500.0 o RESIDUAL (GAMMAS) 50000.0 50200.0 50400.0 50600.0 50800.0 51000.0 51E00.0 51400.0 MEASURED £ REGIONAL (GAMMAS) 3 m m o t + 3D m c n ;i o X m (D M O c 3) 1 ♦ 3 O X X MEASURED £ REGIONAL (GAMMAS) 50300.0 50500.0 50700.0 50900.0 51100.0 51300.0 -i_________i _________ i i i _________( RESrDUAL (GAMMAS) z x ■ < -500.0 -300.0 -100.0 100.0 300.0 500.0 —I ---------I +Q — ■ I 1 1 ---------1 - ■ , . . . 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University of Southern California Dissertations and Theses

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Asset Metadata

Creator Buffington, Edwin Conger (author)

Core Title The Aleutian-Kamchatka Trench Convergence: An Investigation Of Lithospheric Plate Interaction In The Light Of Modern Geotectonic Theory

Degree Doctor of Philosophy

Degree Program Geological Sciences

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag Geology,OAI-PMH Harvest

Language English

Contributor Digitized by ProQuest (provenance)

Advisor Davis, Gregory A. (committee chair), Gorsline, Donn S. (committee member), Tibby, Richard B. (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c18-882666

Unique identifier UC11363600

Identifier 7331330.pdf (filename),usctheses-c18-882666 (legacy record id)

Legacy Identifier 7331330

Dmrecord 882666

Document Type Dissertation

Rights Buffington, Edwin Conger

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA